TRX 2.5 Illustrated...The TRX 2.5 Racing Engine Flame-out - Occurs when the engine stops running at high RPM. Usually the fault of an excessively lean fuel mixture or glow plug failure

The TRX 2.5 Racing Engine

TRX 2.5 IllustratedAir

FilterHead Protector

Head (Cylinder head)

EZ-StartDrive Unit

EZ-StartMotor

EngineMountLow-Speed

NeedleThrottle

Arm

ClutchBell

Flywheel

Carburetor

Air Intake

Fuel Intake

High-Speed Needle

Idle SpeedScrew

EZ-StartPlug

PositiveWire

NegativeWire

Fuel Line

Fuel Tank

Pipe

ExhaustTip

PressureLine

GroundWire

Glow PlugWire

EZ-StartController

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Crankshaft

Crankcase


Terms to KnowYou’ll find these Nitro R/C engine terms throughout thissection of the manual.

.15 - .15 or “15” refers to the size of the engine. The TRX 2.5 is .15cubic inches or 2.5 cubic centimeters (cc). The name “TRX 2.5”is derived from the cc measurement.

ABC - Abbreviation for aluminum, brass, and chrome. Refers toengine construction that consists of an aluminum piston thatslides in a chrome-plated brass sleeve. The TRX 2.5 uses ABCconstruction.

Air filter - The air filter sits atop the carburetor and preventsharmful dust and dirt from entering the engine. Dirt ingestionis the number one cause of premature engine failure so theengine should never be run without the air filter in place.

Big Block .15 - A .15 (2.5) engine that uses a larger crankcasesize and longer stroke than typical .15 engines. Generally onlyused for specific racing classes.

Break-in - Break-in is the procedure for running a brand newengine according to specific instructions. This correctlyprepares the engine for normal running. The break-inprocedure can be different for different makes of engines.Follow the Traxxas directions for break-in exactly.

Carb - Abbreviation for carburetor.Carburetor - The carburetor atomizes (mixes) the fuel with the

air so that the engine can burn it. There are two types ofcarburetors, slide carbs and barrel carbs. The TRX 2.5 uses thesuperior slide carburetor design.

Clean-out - Cleaning-out is a condition that occurs when theengine is accelerating and the fuel mixture becomessufficiently lean to allow the engine to continue into its upperRPM power band. Usually characterized by a noticeabledecrease in blue exhaust smoke and a dramatic increase inengine speed.

Combustion chamber - The combustion chamber is machinedinto the bottom of the cylinder head. This is where the glow

plug ignites the fuel. The shape of the combustion chamber isdesigned to promote more efficient burning of the fuel.

Connecting rod - The connecting rod transfers the pistonmotion to the crankshaft. The TRX 2.5 racing engine uses a“knife-edged” connecting rod. The aerodynamic, sharpenededges allow it to “slice” through the pressurized air/fuelmixture inside the crankcase.

Cooling fins - The cooling fins are molded into the cylinderhead and crankcase and cause heat to be drawn away fromthe engine. Heat is removed when it dissipates into the airpassing across the cooling fins. It is important to keep the finsclean of dirt and debris for maximum cooling efficiency.

Crankcase - The engine “body” that contains all of the runningmechanical components.

Crankshaft - The main shaft of the engine that contains therotating assembly.

Cylinder head (head) - The finned aluminum part on top of theengine that is responsible for dissipating most of the engine’sheat. The combustion chamber is machined into the bottom ofthe head.

Dyno - Abbreviation for dynamometer. A precise piece oftesting equipment that accurately measures engine powerand torque output over the engines entire RPM range.

EZ-Start - Second generation Traxxas on-board electric startingsystem. The system consists of a hand held starter control unitand an on-board gearbox with an electric motor to spin theengine. The new EZ-Start contains many performance andreliability improvements over the first generation EZ-Start.

Filter foam - The oiled foam element inside the air filterhousing. The filter foam in the TRX 2.5 must be thoroughlycleaned and re-oiled after every hour of run time.

Fit - Usually refers to the fit of the piston and sleeve. If the fit istight, then the piston will feel very tight at top of the sleeveand the engine will have good sealing and compression. If thefit is loose, then compression will be low and the piston andsleeve should be replaced.

Learn terms relatedto the TQ-3 RadioSystem on page 12.

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Flame-out - Occurs when the engine stops running at highRPM. Usually the fault of an excessively lean fuel mixture orglow plug failure.

Fuel - (10% 20%) The TRX 2.5 must have model engine fuel torun. Traxxas Top Fuel is recommended. Fuel is sold in quartsand gallons from hobby dealers. The 10 and 20% labelingrefers to the percentage amount of nitromethane contained inthe fuel (see “nitro percentage” definition).

Fuel mixture - The ratio of fuel to air as determined by theneedle settings of the carburetor.

Fuel tubing (fuel line) - The thick silicone tubing that carriesfuel from the fuel tank to the carburetor.

Glow plug - The glow plug is located in the cylinder head at thetop of the combustion chamber. It contains a platinumelement that glows red hot when voltage is applied. When theengine is being started, the heat from the glow plug ignitesthe fuel mixture and starts the combustion process.

Glow plug driver - This tool clips onto the glow plug andsupplies the required voltage to light the glow plug element. Itis also called an igniter. EZ-Start equipped engines do notrequire this separate tool.

Header - The aluminum tube that connects the exhaust systemto the engine exhaust port. The length and diameter of theheader must be carefully selected to extract the most powerfrom the engine.

High-speed needle - Adjusts the carburetors fuel/air mixture athigh RPM.

Idle speed - The speed (RPMs) the engine runs at when thetransmitter’s throttle trigger is at neutral.

Idle speed screw - Located on the carburetor body.Thi screw adjusts the idle RPM of the engine.

Lean - A running condition where the engine is not gettingenough fuel (for the available air). Symptoms include engineoverheating, or the engine runs for a short time and then

stalls, particularly at high speed. This is a dangerous condition that should be corrected immediately or it canruin your engine.

Leaning the mixture - Turning either the high speed and/orlow-speed needle(s) clockwise to decrease the amount of fuelthe engine receives.

Low-speed needle - Needle valve that controls the low-speedfuel mixture.

Needle valve - Valve consisting of a tapered needle that closesagainst a corresponding seat to regulate fuel flow.

Nitro - Abbreviation for nitro methane, a component of modelengine fuel that improves fuel combustion and power output.Nitro also refers to a class of RC powered by model enginesinstead of electric.

Nitro content - The amount of nitro methane used in the fuel.Usually measured as a percentage of the total fuel volume.Traxxas engines are optimized to use 10-20% nitro. 30% nitromay be used for racing.

Nitromethane - Nitro methane is a component in the fuel thatincreases power from the combustion process up to a point.Engines are generally optimized to use a range of nitrocontent for the best power.

O-ring - Rubber “O”-shaped ring used as a sealing gasket.Pipe - Abbreviation for the tuned exhaust pipe on a nitro

engine. See “Tuned Pipe” definition.Piston - The piston is the internal engine part that is attached to

the upper end of the connecting rod and moves up and downin the cylinder sleeve. The precise fit between the piston andthe sleeve creates a seal that allows engine to have therequired compression for combustion.

Port - Ports are openings in the sleeve that allow atomized fuelto enter the combustion chamber and burned exhaust gassesto exit. The shape and location of the ports are a large factor incontrolling the engine timing and power output.

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Priming - Manually causing fuel to move from the fuel tank upto the carburetor. This is sometimes necessary after the enginehas been sitting for a long period of time and all the fuel hasdrained back to the tank. On a Traxxas model this is done byholding your finger over the exhaust tip for one or twoseconds while the engine is starting.

Punch - A term that refers to how quickly the model respondsto throttle input or how quickly it accelerates.

Rich - A running condition where the engine is getting toomuch fuel for the available air. It is better to run an engineslightly rich to increase engine life. Excessively rich mixturescause the engine to have sluggish performance withexaggerated blue smoke and unburned fuel coming from theexhaust.

RPM - Abbreviation for revolutions per minute (how many timesthe engine crankshaft spins in a minute).

Sleeve - Internal engine part that contains the piston. Theprecise fit between the sleeve and the piston creates a sealthat allows engine to have the required compression forcombustion. The sleeve in a TRX engine is made of brass and isthen hard-chrome plated.

Slide carburetor - The throttle on a slide carburetor closes andopens by sliding a barrel in and out of the carburetor body.This type of carburetor is preferred for performance usebecause it provides a less restrictive “straight-through” air paththan the barrel carburetor design.

Stall - When the engine stops running, usually due to anincorrect fuel mixture setting or running out of fuel.

Tuned pipe - The tuned exhaust pipe usually consists of aspecially-shaped metal or composite chamber with bafflesthat is designed to enhance the power output of the engine.

Wear-in - Fitment process that occurs during engine break-inwhere internal engine parts develop an even more precisematched fit through actual use under controlledcircumstances.

WOT - Abbreviation for wide-open throttle.


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The FuelUse the Right FuelIt’s imperative that you use the correct fuel inyour TRX 2.5 for maximum performance andengine life. Traxxas Top Fuel should be used to ensure correct engine lubrication,performance, and ease of tuning. Traxxas TopFuel has been proven in thousands of engines,so you can count on it every day for greatperformance.

Top Fuel is the only fuel which is 100% certified for use inTraxxas engines.Traxxas Top Fuel is made with just the right balance of thehighest grade natural and synthetic lubricants to allowexcellent throttle response and the best top-endperformance, without sacrificing long-term durability.All of the components in the fuel are carefully selected fromthe best materials available and then custom blended tomatch the metallurgy and temperature characteristics ofTraxxas engines.

You may use 10% or 20% nitro-content fuel. Use the samepercentage all the time; don’t switch back and forth between10% and 20% fuel. If you break-in your engine on 20% fuel, thenalways use 20% fuel.

What about Other Fuels?Can other brands of fuel be used besides Top Fuel? There areother fuels that can provide satisfactory performance; howeverthere could be long-term costs in the form of decreased engineperformance, loss of tuning ease, and shorter engine life.

Everyone has an opinion or a claim to make about fuel. Theengineering team at Traxxas spent over 2-years developing theTRX 2.5 racing engine. No one knows more about the specificfuel requirements of Traxxas engines, than Traxxas engineers. Westrongly urge you not to take chances with your engineinvestment and use the Traxxas fuel made for the TRX 2.5.

Handling the FuelFollow all directions and warnings on the fuel can.Keep the fuel tightly capped at all times. Some componentsin the fuel can evaporate very quickly and upset the balanceof the fuel.Do not store unused fuel in the fuel dispenser. Immediatelyreturn fresh unused fuel back into the fuel can.Do not mix old and new fuel. Never mix different brands offuel together.Store the fuel in a cool dry location, away from any source ofheat, ignition, or combustion.Read and follow the safety precautions on page 5in this manual.

Filling the Fuel TankUse a fuel dispensing bottle (Traxxas TopFueler, part# 5001) to put fuel into theSportMaxx’s fuel tank. To fill the fuel bottle,squeeze the air out, insert the dispensertip into the fuel can, and release your gripon the bottle. As the bottleexpands, fuel will bedrawn into it.

To fill your model flip upthe spring-loaded cap onthe fuel tank, insert the tipof the fuel bottle, andsqueeze to dispense thefuel. Fill the tank until thefuel level reaches the base of the filler neck. Close the fuel tanklid, making sure it closes tightly.

Fuel Tank Seal AdjustmentThe rubber seal on the fuel tank is important to the function ofthe engine. The fuel tank is pressurized by the exhaust system toprovide reliable fuel flow. If the tank lid does not seal properly,an air leak will be created that can cause your engine to runerratically and be difficult to start. If necessary, the rubber O-ringtank seal can be adjusted for improved sealing by tighteningthe screw on the underside of the tank lid.

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You may use highernitro percentagesthan 20% in certain

circumstances. Call 1-888-TRAXXAS for moreinformation.

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The Air FilterThe TRX 2.5 air filter is carefully designed to deliver maximumperformance while protecting your engine from dust and dirt.Use only the supplied filter. You will not improve engineperformance by switching to an aftermarket filter, and youmay risk engine damage due to poor filtration.

The TRX 2.5 air filter assembly consists of 3 pieces:

1. A rubber filter base

2. A plastic housing consisting of a permanently assembledmesh cap and body

3. An oiled foam element

You must clean the filter after every hour of runtime, even if thefilter looks clean. Dust (which is often too fine to see) and dirtconstantly move through the filter anytime the engine isrunning. Even if you can’t see dirt on the filter, it is present insidethe foam after any amount of runtime. If you exceed therecommended cleaning intervals, your engine will be damaged.Engine damage or wear due to dirt ingestion is easy to detect,and one of the top causes of premature engine failure.

Air Filter Cleaning Instructions1. Remove the air filter from the

carburetor bore by pulling the entire filter firmly to theside to release it. Do not pullstraight up.

2. Disassemble the filter. Pull therubber base out of the filterbody.With the base removed, the foam element is visible inthe bottom of the filter body. Pull out the foam element.

3. Clean the filter parts by thoroughly washing all three pieces ofthe filter assembly in hot soapy water (dishwashing detergentworks well). Repeat twice.

4. Thoroughly dry the parts with a clean towel or compressed air.Remember to wear your safety glasses when working withcompressed air.

5. Oil the foam element by saturating it with foam filter oil. Usethe supplied Traxxas filter oil (part# 5263) or a high-quality,special-purpose foam filter oil like what is used for high-performance motorcycle and ATV engines.This type of filter oilis available at motorcycle pro-shops. If foam filter oil is notavailable, clean 30-40 weight motor oil can be substituted, butis not preferred. Never run the engine without a properlyoiled filter! Apply 30 drops of the Traxxas filter oil evenly tothe top, bottom and sides of the filter element (30 total dropsdivided among the 3 surfaces). Squeeze the filter elementrepeatedly to help spread the oil throughout. Squeeze theexcess oil from the foam.The filter element should be evenlycolored by the oil. Even color indicates that the oil is evenlydistributed. Note: Do not use the air filter oil for anythingother than the air filter. It is not meant to be a lubricant.

6. Reassemble the filter and install it on the engine, making surethe rubber base fits securely on the carburetor with no gaps orair leaks.


Clean your air filterafter every hour ofruntime to avoid

engine damage, even if thefilter looks clean.

If you usecompressed air todry your air filter

assembly, wear safetyglasses and avoid directingcompressed air towardyour skin.

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The CarburetorUnderstanding the Carburetor adjustmentsThe carburetor performs several functions. It controls theengine’s speed by restricting the intake of air and fuel into theengine. It atomizes the fuel (suspends the fuel droplets in theair) and also controls the air/fuel ratio of the mixture enteringthe engine (how much air for a given amount of fuel).

To help provide a better understanding of engine tuning andwhy it’s necessary, the following is a brief explanation of theair/fuel combustion process that takes place inside the engine.

In order to create the cylinder pressure that results in power, theengine burns the air/fuel mixture. Both air and fuel, in correctamounts, are needed for proper combustion. It is thecarburetor’s job to mix the air and fuel together (atomize thefuel), in the correct proportion for the best possible combustion.This is the ideal air/fuel ratio. The ideal air/fuel ratio required forthe engine remains roughly constant. Due to variations inatmospheric conditions (temperature, humidity, altitude etc.)fuel flow adjustment valves (called fuel mixture needles) arerequired to meter the fuel and maintain the ideal air/fuel ratio inthese ever-changing conditions. For example, colder air is moredense (more air molecules) for a given volume of air andtherefore requires more fuel (more fuel molecules) to maintain

the correct air/fuel ratio. Warmer air is less dense (fewer airmolecules) and therefore needs less fuel to maintain the correctair/fuel ratio. The tuning needles are there to adjust how muchfuel is made available for the carburetor to mix with theavailable air (atomization).

The Fuel Mixture NeedlesThe amount of fuel metered and atomized by the carburetor iscontrolled by the two mixture needles, the high-speed needleand the low-speed needle. The low-speed needle is used tometer the fuel used by the engine at idle and low RPM (part-throttle) engine speed. The high-speed needle is used to meterthe fuel when the throttle is open from part throttle to wide-open throttle (WOT). Two needles on the TRX 2.5 provide precisecontrol of the air/fuel ratio across the engine’s entire RPM range.

The maximum possible fuel flow is always controlled by thehigh-speed needle. It works like the main water valve on agarden hose. Turn it clockwise to close the valve, counter-clockwise to open it. When the throttle is at idle or partiallyopen, the low-speed needle again meters the fuel flow at theoutlet (needle seat) where the fuel enters the carburetor venturi.This second valve acts like the spray nozzle at the end of thegarden hose in our example. When you accelerate from idle, thethrottle opens and the low-speed needle is pulled away fromthe needle seat. This allows more fuel to flow with the increasedair flow. As the throttle is increased, the low-speed needle is

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See page 35 formore informationon how air density

affects engine tuning.

Air

Fuel

Dense Air Less Dense Air

pulled completely away from the needle seat leaving it fullyopen. At that point, fuel metering is entirely controlled by thehigh-speed needle. Again, using our water hose example, whenthe spray nozzle at the end of our garden hose is fully open,then the main water valve can be used to adjust how fast thewater flows.

The engine’s performance is directly linked to the fuelmixture. Richening the fuel mixture increases the amount offuel in the air/fuel mixture ratio and leaning the fuel mixturedecreases the amount of fuel in the air/fuel mixture ratio.

Slightly lean fuel mixtures deliver stronger, more efficientcombustion and more power, but with less lubrication.

Slightly rich fuel mixtures deliver cooler running and morelubrication but with slightly less power.

Tuning the engine means finding the perfect balance betweenthe two; excellent power to meet your needs while maintaininggood lubrication for long engine life. The optimal fuel mixturesetting is rich to provide a safety margin against having a leancondition if some variable changes (such as the temperaturefrom one day to the next).

General fuel mixture settings are measured by the number ofturns the needles are turned out from fully closed. The fuelmixture settings have been pre-set from the factory to typicalbreak-in settings. Do not readjust your carburetor from thefactory settings until after the engine is started and running,and you have been able to observe the engine running toassess what minor adjustments may be required to compensatefor fuel, temperature, and altitude. Adjustments are usuallymade in 1/8 or 1/16-turn increments.

The Idle Speed AdjustmentThe idle speed screw controls the closed position of the throttleslide. When the throttle servo is in its neutral position, thethrottle slide should be stopped against the idle adjustmentscrew. Always use the idle speed adjusting screw to controlengine idle. Do not use the throttle trim on the transmitter toadjust idle speed. The idle speed should be set as low aspossible and still maintain reliable running.

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Water Valve(Controls Overall Flow)

High Speed Needle

Water Nozzle(Controls Fine Flow)

Low Speed Needle

See Tuning the TRX2.5 for BestPerformance on

page 34 for completeinformation on adjustingthe air/fuel mixture andidle speed.

If your factorypreset carburetoradjustments have

been tampered with, usethe following settings: setthe low-speed needle sothat the screw head is flushwith the end of the slide.Set the high-speed needleto 4 turns out from closed.Always use the factorysettings for initial starting.Only use these settingswhen the factory settingshave been lost.

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Lean Rich


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The Traxxas EZ-Start Electric Starting SystemThe Traxxas EZ-Start brings the convenience of push-buttonelectric engine starting to your SportMaxx. The EZ-Start consistsof a handheld control unit and an on-board motorized starter.

Power for the EZ-Start system comes from a 7.2-voltrechargeable NiCad battery pack installed in the handheldcontrol unit (battery not included).The engine glow plug is heated automatically by theEZ-Start system, eliminating the need to keep up with aseparate glow plug igniter.The voltage to the glow plug is kept constant, regardless ofthe load placed on the starter by the starter motor.The “Glow Plug” LED (light emitting diode) on the controlunit indicates the condition of the glow plug.The “Motor” LED indicates the status of the EZ-Start electricstarter motor.The cush drive mechanism in the drive unit preventsdamage to the gears caused by engine kickback.Smart Start™ protection circuitry prevents damage to themotor by cutting power if the load on the motor or otherelectronics exceeds safe limits.

Installing the EZ-Start BatteryThe EZ-Start system requires a fully charged 7.2-volt NiCadbattery pack (not included). Use a charger (not included)designed for 7.2-volt battery packs. Charge the batteryaccording to the charger manufacturer’s directions.

1. Press the tab in the end of the battery compartment door to open

2. Plug a fully charged 7.2-volt NiCad battery pack into theconnector inside.

3. Twist the battery 2 or 3 times to twirl the battery plug wires.This helps hold the wire and battery in place when thebattery is placed in the compartment

4. Place the battery into the compartment and press the wiressecurely into place.

5. Slide the battery compartment door back on and lock theend tab.

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Use the Right ChargerThe most convenient

type of charger is an AC peak-detecting charger that plugsdirectly into an AC walloutlet. It contains specialpeak-detection circuitry thatautomatically shuts thecharger off when the batteryis fully charged.

If you’re using a 15-minutetimed charger, always fullydischarge the battery packbefore each charge. Somehigh mAh battery packs(1500 mAh or higher) requiremore than the standard 15minutes of charge time. If thebattery pack is cold after 15minutes of charging, addanother 5 minutes of chargetime. Closely monitor thebattery pack and stopcharging it when it begins tofeel warm to the touch. Neverleave a battery chargingunattended. Always followcharger manufacturer’sinstructions.


Using the EZ-StartYour EZ-Start controller plugs into a 4-prong receptacle in thecenter of the pickup bed on your SportMaxx. When the redbutton on the controller is depressed, the EZ-Start motor beginsto spin the engine, and power from the control unit heats theglow plug. Assuming all settings and preparations are correct,the engine should start almost immediately.

Each of the two status indicatorLEDs on the handheld control unit,the Motor LED and the Glow PlugLED, should light green whilestarting. If either LED fails to lightwhile starting, there is a faultindicated with that function:

If the Glow Plug LED fails tolight, the glow plug may be bad,or the glow plug wire may bedamaged or disconnected.

If the Motor LED fails to lightand the starter fails to operate,then the EZ-Start is inprotection mode.

Protection ModeThe EZ-Start uses Smart Start™ technology to monitor thecondition of the system and detect failures. The controllermonitors the load being placed on the EZ-Start motor. If theload becomes excessive, the system shuts off power to themotor to prevent costly damage to the motor and thecontroller. This may occur, for example, if the engine floods withfuel during starting. The starter spins at first but when excessivefuel in the combustion chamber begins to lock up the engine,the starter motor slows under the heavier load. This causes theprotection circuit to shut off the power to the motor. Allow atleast 3 minutes for the starter motor to cool and the circuit toautomatically reset before continuing. Use the time to find andeliminate the condition that caused the excessive load on thestarter motor.

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When the EZ-Startcontroller is inprotection mode, wait

at least three minutes beforeattempting to start theengine, to give the startermotor time to cool.

It’s normal for yourEZ-Start controller to become warm

after repeated use.

See page 43 for information on clearing a

flooded engine.

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See ImportantPoints to Rememberon page 5 for other

precautions.

Never run yourSportMaxx indoors.Since the TRX 2.5

racing engine exhaustfumes are harmful, alwaysrun your SportMaxxoutdoors, in a well-ventilated area.

Your TRX 2.5 racingengine doesn’tusually require

priming. If you do need toprime your engine, watchthe fuel line carefully toavoid flooding your engine.See page 43 forinformation on clearing aflooded engine.

Your carburetor ispre-set at thefactory to give the

correct air-to-fuel ratio andidle speed for enginebreak-in. Do not adjust thecarburetor unless youobserve a poor runningcondition that requirescorrection.

Breaking-in Your TRX 2.5 Racing EngineThe TRX 2.5 uses a ringless, aluminum-brass-chrome (ABC)piston/sleeve construction.This type of engine design relies on avery precise running fit between the piston and sleeve for cylindersealing. Engine break-in is necessary to allow the piston andsleeve to develop an extremely precise fit and optimum cylindersealing. Therefore, proper engine break-in is critical to achievingthe fastest, most reliable engine performance.

Allow yourself about 1 to 11/2 hours to complete the break-inprocedure.The engine break-in period will take 5 tanks of fuel in aSportMaxx.The break-in time is not the time to impress yourfriends with your new SportMaxx. You must wait until the engineis fully broken in before attempting sustained high speedrunning. Patience and careful attention during break-in will rewardyou with the best-performing TRX 2.5 possible.

During break-in, your engine may appear to malfunction withsymptoms like stalling, inconsistent performance, and fouled glowplugs.These are simply the normal “break-in pains” enginessometimes go through.They will disappear once your engine isfully broken in. Many owners report not experiencing any of thesesymptoms with the TRX 2.5. We recommend replacing the glowplug with a new one after the engine break in procedure.

Engine Break-in ProcedureThe focus during break-in is to vary and limit the engine speed.This will be accomplished by accelerating and stopping at differentrates for the first 5 tanks of fuel. As the engine begins to break-in,the duration and intensity of the acceleration will graduallyincrease. Sustained high-speed running is not permitted until the6th tank of fuel. Perform the initial break-in on a large, flat, pavedsurface. Apply all throttle and braking actions gently. Abruptacceleration or braking could cause the engine to stallunnecessarily.

Special break-in fuels are not recommended. Use the same fuelyou plan to use everyday.If possible, avoid breaking-in the engine on extremely hot orcold days.Pay careful attention to the fuel level. Do not allow the fuel tank

to run completely empty. An extremely low fuel level causesthe mixture to run too lean.This could result in a burned glowplug or extremely high engine temperatures.Keep extra glow plugs handy (Traxxas part #3231).The break-inprocess can cause deposits to form on the plug leading to plugfailure.

Follow the instructions exactly for each of the first 6 tanks of fuel.

Starting Your TRX 2.5 Racing Engine for the First TimeBefore you start your TRX 2.5 racing engine for the first time, makesure you have read all instructions and precautions in this manual.Pay close attention to the tank-by-tank break-in instructions inthe next section, and make sure you have read and understoodthem before you run your engine.

Your engine must be at room temperature (70°F or 21° C) orabove the first time you start it. If it’s cooler than roomtemperature outside, keep your SportMaxx indoors until you’reready to start it, then take it outside.

1. Turn on the radio system according to the instructions on page 18.

2. Make sure the throttle is in the idle position.3. Connect the EZ-Start controller according to the instructions on

page 31.4. Press the starter button and watch for fuel moving through the

fuel line up to the carburetor.Watch closely! The fuel moves veryfast. If the fuel doesn’t move through the line within 5 seconds,prime the engine by briefly (one or two seconds) covering theexhaust outlet until the fuel is just visible in the carburetor fuelline. Watch carefully! If the engine is primed too long, it willflood with fuel and stop turning.

5. Once fuel reaches the carburetor, the engine should quickly startand idle.

6. Disconnect the EZ-Start controller from the model.7. Proceed with the engine break-in.

If your engine doesn’t start, see Troubleshooting Your SportMaxxon page 42.

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As you gainexperience in thehobby, you may

discover that many peoplehave differing opinions onwhat is the properprocedure to break-in amodel engine. Only use theTraxxas break-in procedure.Other break-in procedurescould result in a weak,damaged, or otherwise poorperforming engine. Theprocedure outlined herewas extensively tested andproven to yield betterperforming engines thanother “common” break-inmethods. Even if you haveyears of experience usingmodel engines, please donot ignore this caution!

Tank 11. Drive the model with the body off.2. Driving procedure: Gently pull the throttle trigger to 1/4

throttle over a 2-second count. Then gently apply the brake tostop. Count the two seconds out while accelerating: onethousand one, one thousand two, and then stop. Operate thethrottle trigger as smoothly as you can. Repeat this starting andstopping procedure until the first tank of fuel is nearly empty.

3. Look for thick blue smoke exiting the exhaust outlet. If there isno smoke, richen the high-speed needle 1/4 turn, by turning theneedle counterclockwise.

4. When the fuel tank is nearly empty, shut off the engine bypinching the fuel line connected to the carburetor.

5. Let the engine cool for 15 minutes.Note: If at any point the engine cuts out or stalls during gentleacceleration, richen the high-speed needle 1/4 turn by turning theneedle counterclockwise.

Tank 21. From tank 2 forward, the SportMaxx should be driven with the

body on.2. Driving procedure: Gently pull the throttle trigger to 1/2

throttle over a 2-second count. Then gently apply the brake tostop. Count the two seconds out while accelerating: onethousand one, one thousand two, and then stop. Repeat thisstarting and stopping procedure until the second tank of fuelis nearly empty.

3. When the fuel tank is nearly empty, shut off the engine and let itcool for 15 minutes.

Tank 31. Driving procedure: Gently pull the throttle trigger to 1/2

throttle over a 3-second count. Then gently apply the brake to stop. Count the three seconds out whileaccelerating: one thousand one, onethousand two, one thousand three, and thenstop. Repeat this starting and stoppingprocedure until the third tank of fuel isnearly empty.

2. As the engine loosens, the idle speed mayincrease and cause the model to try to creepforward when stopped. Reduce the idle

speed by turning the idle adjustment (see page 22) on thecarburetor counterclockwise.

3. When the fuel tank is nearly empty, shut off the engine andrefuel. From here on, you do not need to let the engine coolbetween tanks.

Tank 41. Driving procedure: Gently pull the throttle trigger to full

throttle over a 3-second count. Then gently apply the brake tostop. Count the three seconds out while accelerating: onethousand one, one thousand two, one thousand three, and thenstop. Repeat this starting and stopping procedure until thefourth tank of fuel is nearly empty.

2. Apply the throttle gradually! Your finger should not reach fullthrottle until the end of the three-second count.

3. Keep your driving smooth and consistent.4. When the fuel tank is nearly empty, shut off the engine and

refuel.

Tank 51. Driving procedure: Gently pull the throttle trigger to full

throttle over a 3-second count, hold for 2 more seconds, andthen gently apply the brake to stop. Count the five seconds outwhile accelerating. Repeat this starting and stoppingprocedure until the fifth tank of fuel is nearly empty.

2. When the fuel tank is nearly empty, shut off the engine andrefuel.

Tank 6During the sixth tank of fuel, the engine can be tuned for generalperformance use. Proceed to the next section in this manual.

Tank12345

Throttle1/41/21/2FullFull

Time2 Seconds2 Seconds3 Seconds3 Seconds5 Seconds

Cool15 Minutes15 Minutes

---

BodyOffOnOnOnOn

NotesApply throttle gradually.Apply throttle gradually.Reduce idle speed if necessary.Keep your driving consistent.Accelerate over 3 second count,hold for 2 seconds.

34


When adjusting thelow-speed fuelmixture, it is very

important to make severalhigh-speed runs with theSportMaxx betweenadjustments to clear out anyexcess fuel. Perform thepinch test immediately after.If the engine is allowed toidle for a long period of time,it could “load up” with fueland give you an inaccuratemeasurement from yourpinch test.

For yourconvenience, thelow-speed needle

has a positive stop thatprevents it from being overtightened and damaging theneedle and seat. This alsoprovides an easy way togauge how many turns outfrom closed the low-speedneedle adjustment is set to.

When tuning forperformance, watchclosely to notice

when there is no longer anyincrease in speed or powerwhen the high-speedmixture is lean. If you leanthe high-speed mixture tothe point that the enginecuts-out, hesitates, or stalls,you are well into the dangerzone and engine damage islikely. Richen the high-speedneedle 1/4 turn and retune.

Tuning the TRX 2.5 for Best PerformanceThe engine’s performance depends on the fuel mixture. Turn themixture needles clockwise to lean the fuel mixture andcounterclockwise to richen it. Leaning the fuel mixture willincrease engine power up to the engine’s mechanical limits.Never run the engine too lean (not enough fuel flow). Neverlean the engine until it begins to cut-out or stall. Leaning theengine beyond the safe allowable limits will result in poorperformance and almost certain engine damage. Indicationsof an overly lean mixture include:

Cutting out or sudden loss of power during acceleration. Overheating (temperature beyond 270° F at the glow plug)Little or no blue smoke coming from the exhaust.

If any of these conditions are present, stop immediately andrichen the high speed mixture 1/4 turn. The engine willprobably be slightly rich at that setting and you can then retunefor performance. Always tune for performance by starting richand moving leaner toward the ideal setting. Never try to tunefrom the lean side. There should always be a light stream of bluesmoke coming from the exhaust.

Before you begin tuning, the engine should be warmed up to itsnormal operating temperature and running slightly rich. All finaltuning adjustments must be made to the engine at its normaloperating temperature. You can tell the engine is running richby noting any of the following:

Sluggish acceleration with blue smoke coming from the exhaust.There is unburned fuel spraying from the exhaust tipLeaning the high-speed fuel mixture increases performance

High-Speed Fuel Mixture AdjustmentWith the engine warm and running at a rich setting, graduallylean the high-speed fuel mixture in 1/16 turn increments. Makeseveral high-speed passes with the SportMaxx after eachadjustment to clear out the engine and note any change inperformance. The TRX-2.5 is extremely powerful. Remember toapply the throttle gradually to prevent wheelies or loss of

control. Continue this procedure until one of the followingconditions exist:

1. There is no longer any performance improvement2. The engine begins to cut out at high speed(Danger!)3. There is a sudden loss of power during acceleration (Danger!)4. The engine begins to overheat. Symptoms of

overheating include:

Steam or smoke coming from the engine (not exhaust)Hesitation or stalling during accelerationPopping or clattering sound when decelerating(detonation)Fluctuating idle speedTemperature measurement above 270° F at the glow plug

If any one of the above conditions occurs, the fuel mixture isalready past the maximum safe lean setting. Richen the fuelmixture to the optimum setting by richening the high-speedneedle at least 1/8 turn counterclockwise and retest. This settingwill extend engine component life.

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35

Low-Speed Fuel Mixture AdjustmentThe low-speed mixture is always set after the high-speed needleis correctly adjusted. The low-speed mixture will be set using thepinch test.

1. Once the engine is warm, do several high-speed runs toconfirm that the high-speed needle is set correctly.

2. Bring the vehicle in and pinch closed the fuel line going intothe carburetor. The engine should run for 2-3 seconds, speedup, and then die.

3. If the engine runs longer than 3 seconds, then lean thelow-speed needle 1/16 turn, make several more high-speed runs, and retest.

4. If the engine dies immediately without speeding up, thenrichen the low-speed needle 1/8 turn, make several morehigh-speed runs, and retest.

When the low-speed needle is set correctly, the engine’s throttleresponse should be very quick, possibly even to the point ofmaking it difficult to keep the SportMaxx from doing a wheeliewhen you accelerate!

Idle Speed AdjustmentOnce the high and low-speed mixtures have been set, reducethe idle speed to the minimum reliable idle speed. Remember,this adjustment should be made while the engine is running atnormal operating temperature.

1. Turn the throttle trim on the transmitter so that the brakesare applied. This ensures that the throttle slide is restingagainst the idle adjustment screw.

2. If necessary, remove the air filter to gain access to the idleadjustment screw.

3. Turn the screw counterclockwise to reduce the idlespeed, or clockwise to increase it. The idle speed shouldbe set as low as possible while still maintaining reliablerunning characteristics.

4. Reset the throttle trim on the transmitter

Fine-Tuning the CarburetorAfter fine-tuning your TRX 2.5 racing engine at the end of thebreak-in procedure, no major adjustments to the fuel mixtureare usually necessary. Make note of the temperature, humidity,and barometric pressure at the time you finished fine tuningyour carburetor. Current weather conditions can be foundonline from national websites, local TV news websites, andTelevision. This information will be considered your baselinesetting. You may need to adjust your carburetor needles tocompensate for changes in temperature and barometricpressure (air density) from day to day. Generally, you’ll need torichen the fuel mixture when the weather is colder than yourbaseline temperature and the air density is higher. Lean the fuelmixture when weather is warmer than your baselinetemperature and the air density is lower. The chart belowprovides general guidelines on how weather conditions affectair density when they move higher or lower than your baselinesetting (see page 28 for detailed info on how air density affectsmixture settings).

If the...Humidity

Pressure (barometer)

Temperature

Altitude

Nitro %

is..LowerHigherLowerHigherLowerHigherLowerHigherLowerHigher

then the air density is...Slightly more denseSlightly less denseLess denseMore denseMore denseLess denseMore denseLess dense

adjust (correct) the fuel mixture to be...Slightly richerSlightly leanerLeanerRicherRicherLeanerRicherLeanerLeanerRicher

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Tuning The Engine By TemperatureThe following procedures require anoptional infrared temperature probeor on-board temperature gauge(Traxxas on-board digitaltemperature gauge, part#4090).Engine temperature can be used asan effective tuning aid when you understand the relationshipbetween engine temperature and ambient temperature.

The engine operating temperature, when tuned for maximumperformance, will vary according to atmospheric conditions. Theatmospheric condition that has the most influence on enginetemperature is air temperature. Expect the engine temperatureto vary almost in direct proportion to atmospheric temperature.Assuming you tuned the engine for the same maximumperformance each day, the engine will run about twentydegrees hotter when it’s ninety degrees outside than it would inseventy-degree weather. For this reason, we cannot give you adefinitive temperature range that indicates the best possibleengine tuning.

The temperature gauge can aid you in tuning by giving you arelative indication of how your adjustments are affecting theengine and by preventing you from exceeding maximumengine temperature. For example, as you lean the fuel mixture,the engine performance will increase along with thetemperature. If you continue to lean the fuel mixture and thetemperature increases but the engine performance does notchange, then you have exceeded the maximum safe leansetting.

Even if it’s 100°F outside, you should be able to tune formaximum performance. Try to keep your engine from exceeding270°F when measured at the glow plug. If tuning for maximumperformance results in engine temperature exceeding 270°F, tryto increase airflow tothe engine by cuttingout the rear of thebody, windshield, andfront valance. If theengine temperaturestill cannot be keptbelow 270°F, richenthe high-speedneedle slightly.


37

Driving the SportMaxx

IntroductionYour TRX 2.5 racing engine isbroken in, the fuel mixture isbalanced, and the idle isset…now it’s time to havesome fun! This sectioncontains instructions ondriving and makingadjustments to yourSportMaxx. Before you go on,here are some important precautionsto keep in mind.

Don’t run your SportMaxx in water, mud, snow, or wetgrass. It’s tempting, but water and mud are easily drawnthrough the air filter and will severely damage the engine.Small amounts of moisture can cause electronics to fail andloss of control over your SportMaxx.The TRX 2.5 is extremely powerful. Remember to apply thethrottle gradually to prevent wheelies or loss of control.Don’t hold the SportMaxx off the ground and rev the engineexcessively with no load on the engine. This practice couldresult in internal engine damage. Avoid over-revving theengine when the SportMaxx is airborne after a jump.Avoid excessive high-speed running for extended periods oftime or over long distances. This could cause the engine tobuild up enough speed to exceed maximum safe RPM limits.Don’t drive your SportMaxx with drive train damage of anykind. The engine could be damaged due to overloads on theengine caused by drivetrain friction, or over-revving causedby loose or missing parts.Don’t tow anything with your SportMaxx. The engine iscooled by airflow created by speed. Towing creates a highload on the engine, and at the same time limits cooling ofthe engine due to low vehicle speed.If your SportMaxx gets stuck, stop driving immediately. Movethe vehicle and then continue driving.

Driving TipsMonster trucks by design have a high center of gravity thatrequires a different driving technique. To prevent rollovers,slow down as you approach turns and then apply strongthrottle through the turns. This technique will help theSportMaxx grab the surface and turn sharper.Do not apply brakes and turn the wheel at the same time.You could tip the truck over.When jumping, apply some throttle while the SportMaxx isin the air to keep the truck’s nose up and land level on all 4wheels. Be careful not to over-rev the engine or land at fullthrottle. Either could seriously damage your SportMaxx. Ifthe nose of the truck is too high, then quickly tap the braketo level the truck in the air..Drive over large obstacles (such as curbs and rocks) at anangle, instead of head on. This will allow the suspension toarticulate and absorb the impact much easier.

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Once you become familiar with driving your SportMaxx, youmight need to make adjustments for better driving performance.

Adjusting the Slipper ClutchThe SportMaxx features an adjustable slipper clutch on the spurgear to help protect the drive train from sudden shock loads(such as landing off of jumps with the engine at full throttle).Under normal conditions the slipper clutch should not slip.Before adjusting the slipper clutch, turn the model off. Donot adjust the slipper clutch while the engine is running.

Use the supplied glow plug (universal) wrench to tighten theslipper nut (clockwise) until it stops, and then back the nut out1/4 of a turn. If you notice any decrease in performance aftermaking changes to the slipper clutch adjustment, then it maybe too loose. The slipper must not be allowed to slip duringnormal acceleration or the slipper could be damaged.

Adjusting the Toe-inYour SportMaxx comes from the factory with zero degrees of toe-in in the front, and one degree of toe-in in the rear.You can adjustthe toe-in on the front and rear of the truck. Set the steering trimon your transmitter to neutral. Now, adjust your steering

turnbuckles so thatboth front wheelsare pointingstraight ahead andare parallel to eachother (0 degreestoe-in).This willensure the sameamount of steeringin both directions.Adjust the rear toecontrol links sothat the rearwheels have 1˚ oftoe-in.

Adjusting the CamberTwo pivot balls are accessible throughthe spokes of each of the wheels onyour SportMaxx. From the factory, thepivot balls are completely tightenedinto the suspension arms, which giveeach of the wheels –1˚ of camber.Unscrewing the bottom camber pivotball with a 2.5mm hex wrench willincrease the wheel’s negative camber.You should not adjust the top pivot ball; unscrewing it willincrease positive camber and will also change the wheel’s toe-in.

Adjusting the suspensionThe SportMaxx has adjustable suspension so that it may beoptimized for different kinds of terrain and driving styles.

Fine Tuning the ShocksThe eight shocks (oil dampers) on your SportMaxx havetremendous influence on its handling. Whenever you rebuildyour shocks, or make any changes to the pistons, springs or oil,always do it carefully and in sets (front or rear). Piston headselection depends on the range of oil viscosities that you haveavailable. For example, using a two-hole piston with lightweightoil will give you the same damping as a three-hole piston withheavier oil. We recommend using two-hole pistons with a rangeof oil viscosities from 10W to 40W (available from your hobbyshop). The thinner viscosity oils (30W or less) flow with lessresistance and provide less damping, while thicker oils provide

38

Adjusting Your SportMaxx

0°0°

1°1°

-1° -1°

Factory toe-insettings can beachieved by

installing the rod ends onthe turnbuckles until theybottom out against theshoulder. If you desiremore toe-out, the tips ofthe rod ends must betrimmed to allow them toscrew down further ontothe turnbuckle threads.

39

more dampening. Use only 100% puresilicone shock oil to prolong seal life.From the factory, the SportMaxx uses30W oil.

The ride height for the SportMaxx canbe adjusted by adding or removing theclip-on spring pre-load spacers. Note thatchanges in ride height will occur whenchanges in shock angle or spring ratesare made. You can compensate for rideheight changes by changing the pre-loadspacers on the shocks

Caster AdjustmentThe SportMaxx offers the ability to adjustthe caster angle of the front suspension.Caster adjustment may be used to influence the understeer/oversteer handling characteristics of the SportMaxx. Increasingthe caster angle will increase the tendency of the truck tooversteer (less traction on the rear tires, more traction on thefront tires), while decreasing the caster angle will cause thetruck to have a tendency to understeer (push in the turns). Thiseffect becomes more pronounced at higher steering angles andhigher spring rates. Caster is adjusted by repositioning theshims on the pivot point of the upper suspension arms.

The stock caster setting is 7-degrees with one shim at each endof the arm. Reduce the caster angle to 4-degrees by removing

the rear shim and inserting it next to the front shim. The casterangle can be increased to 10-degrees by removing the frontshim and inserting it next to the rear shim.

Shock Mounting PositionsBig bumps and rough terrainrequire a softer suspensionwith the maximum possiblesuspension travel and rideheight. Racing on a preparedtrack or on-road use requires alower ride height and firmer,more progressive suspensionsettings. The more progressivesuspension settings helpreduce body roll (increased rollstiffness), dive during braking,and squat during acceleration.Upper shock mountingposition (A) should generally be used with lower shockmounting positions 1 and 2. Upper shock mounting position (B)should be generally be used with lower shock mountingpositions 3 and 4. The innermost upper shock mountingposition (0) can be used for tuning with the inner pair of lowershock mounting positions on the arm (1,2). It is not compatiblewith lower shock mounting positions 3 and 4.Othercombinations may be used to achieve individualized suspensionsettings.

Lower Shock Mounting Positions In the out-of-the-box configuration, the shocks are installed inposition (A) on the shock tower and position (2) on the lowersuspension arm. This setting allows for moderate suspensiontravel and ride height. The more vertical position of the shocksallows for lower shock progression and the soft, plush feel that’scharacteristic of a Traxxas Maxx Truck.


7°

Caster adjustment shims (1 Front, 1 Rear)

Vertical

Ground plane

Vertical4°

Caster adjustment shims (2 Front)

Ground plane

Vertical

Caster adjustment shims (2 Rear)

Ground plane10°


The outer pair of holes on the lower suspension arm should beused to lower the ride height of the SportMaxx, and increase thespring force (at the wheel). This setting will improve high-speedcornering on smoother terrain by lowering the center of gravityand providing a firmer suspension feel. Body roll, brake dive, andsquat will be reduced.

Spring rate (at the wheel) increases as the lower shockmounting position is moved from position (1) to position (4).This is equivalent to using stiffer springs. Use higher spring ratesettings for flatter terrain with smaller and fewer bumps, andlower spring rate settings for bigger bumps.

Ride height decreases as the lower shock mounting position ismoved from position (1) to position (4). Each pair of lower shockmounting holes (1,2 and 3,4) has equal ride height. Use lowerride height for high-speed cornering and flat terrain, and when

racing on relatively smooth tracks. Increase the ride height forrougher terrain and tracks.

Upper Shock Mounting Positions The upper shock mounting positions will have suspensioneffects opposite from the lower shock mounting positions.

Spring rate (at the wheel), increases as the upper shockmounting position is moved from position (A) to position (B).

Ride height is not affected by changes in the upper shockmounting position.

Use the chart below to see the effect of the various shockmounting positions. The horizontal length of the lines indicatesthe amount of suspension travel. The angle or slope of the linesindicates the spring rate (at the wheel).

40

For easier access tothe rear-most shockmounting screw,

remove the one end of therear turnbuckle. In the front,remove the suspension pinfrom the lower frontsuspension arm to gaineasier access to the lowershock mounting screws.

2.5

2

1.5

1

0.5

00 10 20 30 40 60 70 80 90 10050

Whe

el Fo

rce (

lb)

Wheel Travel (mm)

Wheel Force vs. Wheel Travel

Lower Mount 1, Upper Mount 0Lower Mount 2, Upper Mount 0Lower Mount 1, Upper Mount ALower Mount 2, Upper Mount ALower Mount 3, Upper Mount ALower Mount 4, Upper Mount ALower Mount 1, Upper Mount BLower Mount 2, Upper Mount BLower Mount 3, Upper Mount BLower Mount 4, Upper Mount B

Less Firm

More Firm

Lower Mount 4

Lower Mount 3

Lower Mount 2

Lower Mount 1

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The following section addresses some very basic engine andradio questions you may have about your SportMaxx. Mostquestions arise from simple user errors or minor adjustments thatare easy to correct. If you can’t find a solution for your SportMaxxhere, then visit our Web site at www.Traxxas.com and click on theCustomer Support menu.There you will find a much moreextensive and detailed online troubleshooting area. In addition,you may call Traxxas Customer Service at 1-888-TRAXXAS (outsidethe US call 972-265-8000).

Radio system does not work properly:If the power light on the transmitter does not come on, checkfor proper battery installation and that the batteries are newand/or fully charged. If the power light is blinking, then thetransmitter batteries are weak and should be replaced. Seepage 13 for more details.If the transmitter light is on but the radio is still notresponding, check for proper installation of the receiverbatteries and that the batteries are new and/or fully charged.Check to make sure the on/off switch on the model is in theon position. Finally, if there is still no response check the redand black wires that connect the battery pack to the “batt”terminal on the receiver (you will have to remove the receivercover). Make sure the wires are not pinched or damaged andthat the plug is secure in the receiver. See page 14 for moredetails.

Short radio range:If the radio range appears short, then first check to make surethe transmitter antenna is fully extended and that theantenna in the SportMaxx is in place and has not been cut ordamaged. Next, make sure the batteries are all fully charged.Finally, if you are still experiencing short range, try a differentlocation. Sometimes there can be interference from varioussources that can cause your radio to malfunction.

Engine will not spin (EZ-Start will not turn the engine):If neither LED on the controller lights, the EZ-Start batterycould be discharged or improperly connected. Inspect andrecharge if necessary.

If the glow plug LED lights and the motor LED does not, thenthe EZ-Start controller is in protection mode. Allow thecontroller to cool for at least three minutes.The circuitryshould automatically reset.Check to make sure the wires are connected to the EZ-Startmotor in the SportMaxx.The red wire should connect to thepositive motor terminal, indicated by a red dot next to theterminal.The engine could be flooded. If too much fuel accumulates inthe combustion chamber at start up, the engine willhydraulically lock. Follow the procedure on page 43 forclearing a flooded engine.Check for binding at the engine flywheel. If you are not able toturn the engine by hand, the engine could be flooded, therecould be binding in the clutch system, or there could beinternal engine damage. (Note: It is normal for the engine tobe extremely tight and hard to turn when the piston reachesthe top of the compression stroke.)

Engine extremely sluggish, hard to start, and will not idleduring tank 1 of the break in:

It is possible that the factory adjusted break-in settings onyour carburetor are too rich for your geographic location,atmospheric conditions, or fuel brand. Extremes intemperature, humidity, barometric pressure, and altitude can’talways be accounted for with a single high-speed needlesetting.The symptoms described above can occur when theair density is very low such as in high mountainous elevations,and extremely cold temperatures. Under these conditions,lean the fuel mixture slightly, 1/8 turn, to see if there is anyimprovement in starting and idling. Only lean the fuel mixturejust until the engine will run and idle reliably and thenproceed with the break in.

The contents of different brands of fuel (other than TraxxasTop Fuel) in combination with extreme atmosphericconditions can also make the factory preset break-in settingstoo rich and cause the symptoms described above. Again, tryleaning the fuel mixture slightly, 1/8 turn, to see if there is anyimprovement in starting and idling.

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Troubleshooting Your SportMaxx

Engine spins but will not start:If the engine is spinning but will not start, first check to makesure that both the motor and glow plug LEDs on the EZ-Startcontroller light when the button is depressed. If the glowplug LED does not light, make sure the blue glow plug wire istightly connected and is not damaged in any way. If the wireis good, then replace the glow plug. It is normal for glowplugs to require periodic replacement. Only use Traxxasheavy-duty long glow plugs (part #3231).Check to make sure the fuel is getting to the carburetor.Remove the fuel line where it connects to the carburetor tosee if there is fuel in it. If not, you may need to prime theengine. Reconnect the fuel line and then refer to page 32 forinstructions on priming the engine.Check your fuel mixture settings. It may be necessary toadjust the fuel mixture if the outside temperature orbarometric pressure has changed significantly since the last time the engine was run (see Fine Tuning theCarburetor on page 36). Turn the high-speed needle out(rich/counterclockwise) 1/4 turn, hold the throttle trigger atabout 1/2 throttle and try again to start the engine. Oncestarted, retune the engine for performance (see page 35).The engine could be worn. If the fit between the piston andsleeve is loose, compression is reduced and the engine will bedifficult to start when it is warm, and may tend to stall whenrunning and when the throttle is closed suddenly to idle.Engine life depends on many factors including fuel type, airfilter maintenance, needle settings, and how the engine wasused. For example, if the engine was allowed to ingest dirtfrom lack of air filter maintenance or running through water,then the internal engine components could wear outextremely fast.

Engine performance sluggish:Engine performance depends mostly on the fuel mixturesettings and how they compensate for the currentatmospheric conditions. Before you suspect other failures withthe engine, richen the high-speed needle at least 1/4 turn andthen retune the engine for performance (see page 35).

If the fuel mixture seems to be set correctly, make sure thefuel is fresh. If the fuel is old, or was left uncapped for a longperiod, then some of the important fuel components couldhave evaporated. Try new, fresh, Traxxas Top FuelTry a new Traxxas 3231 glow plug. Sometimes a glow plugwill work well enough to start the engine but not be able todeliver the engine’s full performance potential.Check to make sure there is no binding in the driveline thatwould cause excessive loads on the engine.

Clearing a Flooded Engine:If the engine is primed for too long during startup, then it canbecome flooded with fuel. When the engine is flooded it will nolonger turn due to excess fuel in the combustion chamberpreventing upward movement of the piston. Use the followingprocedure to clear a flooded engine.

1. Remove the blue glow plug wire.

2. Remove the glow plug and gasket with the glow plugwrench supplied with your model. A 5/16 nut driver will alsowork.

3. Turn the model upside down and plug in the EZ-Start controller.

4. Push the EZ-Start button for several seconds to clear theengine of excess fuel

5. Turn the model over and reinstall the glow plug and gasket.

6. Reconnect the blue glow plug wire to the glow plug.

7. Reconnect the EZ-Start controller

8. Do not prime the engine. Pull the throttle to 1/2 throttle andpush the EZ-Start button. The engine should startimmediately.

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Troubleshooting Your SportMaxx

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If the engine isworn or damagedenough to require

replacing the piston,sleeve, or connecting rod,consider exchanging yourold engine for a brand newengine under the terms ofthe Traxxas Lifetime EngineReplacement Plan (ERP). Itcould save you time andeffort. Details are in yourmodel’s documentationpackage.

The TRX 2.5 isdesigned to be easyto rebuild. Criticalengine components

such as the crankcase,crankshaft, and enginebearings are made toextremely high qualitystandards and shouldunder normalcircumstances outlastmultiple sets of pistons,sleeves, connecting rods,and wrist pins(reciprocating assemblies).It could be moreeconomical for you tocontinue to use your goodbearings and crankshafts,and simply replace thereciprocating assembly asneeded. Engine assembly isnot difficult and replacingthe reciprocating assemblydoes not require anyspecial tools or skills.

Your SportMaxx requires timely maintenance in order to stay intop running condition. Neglecting the maintenance could allowdirt, deposits, and moisture to build up inside the engineleading to internal engine failure. The following proceduresshould be taken very seriously.

After each hour of running:Clean and re-oil the air filter.The instructions for thisprocedure are on page 27. We cannot stress enough thevalue of cleaning your air filter at the scheduled intervals.Do not neglect your air filter maintenance!

Clean the outside of the engine of accumulated dirt, oil, andgrime. Accumulated grime will decrease the engine’s ability tocool itself.

After each running session:Perform after-run maintenance on the engine.This clears theengine of destructive moisture and other corrosive deposits.This is extremely important for the life of the engine. Seepage 45 for after-run maintenance procedures.

Inspect the vehicle for obvious damage or wear. Look for:1. Loose or missing screws2. Cracked, bent, or damaged parts 3. Cut or loose wiring 4. Cut or kinked fuel lines5. Signs of fuel leakage

Inspect the gears for wear, broken teeth, or debris lodgedbetween the teeth.

Other periodic maintenance:Slipper clutch pegs (frictionmaterial):The slipper clutchpegs will wear over time andrequire replacement.The life ofthe pegs depends on how theslipper clutch was adjusted andhow the SportMaxx was used.If the slipper will not tighten or you are seeing signs of wearon the face of the gear, then the pegs should be replaced.

Piston/sleeve: The life of the piston andsleeve will vary greatly with how theengine was used and maintained.Thepiston and sleeve should be replacedwhen they no longer seal effectively(loss of compression). Symptoms includethe engine being difficult to start whenwarm, stalling when warm, and stallingwhen throttle is suddenly closed to idle.Replace the wrist pin and G-clipwhenever the piston and sleeve arereplaced.

Connecting rod: The connecting rodshould be replaced when the piston andsleeve are replaced or after three gallonsof fuel, whichever comes first. Alsoreplace the piston wrist pin and G-clipwhenever the connecting rod is replaced. As with otherinternal engine components, connecting rod life dependsengine’s usage and the quality and frequency of theengine maintenance.

EZ-Start: The cush drive elements in the EZ-Start driveunit should be inspected after 3-gallons of fuel. If the cushdrive elements appear deformed or hardened they shouldbe replaced. Inspect the EZ-Start gears for any signs ofwear. Damaged gears should be replaced. Coat the gearswith a thin layer of white lithium grease.

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Maintaining and Storing Your SportMaxx

Maintaining and Storing Your SportMaxx

After-run ProcedureYou must perform after-run maintenance on your Traxxasengine whenever the model will be stored for longer than a fewhours. Taking the time to prepare your engine for storage willreward you with longer engine life, easier starting, and betterperformance.

When a nitro engine is shut off, some excess unburned fuelremains in the engine. The methanol in model engine fuel ishygroscopic, which means it easily attracts and absorbsmoisture. This moisture can cause rust and corrosion on thesteel engine parts (crankshaft, bearings, wrist pin and startershaft) if the fuel is not removed from the engine. There are afterrun oil products available from your hobby dealer or you canuse WD-40™, a common household lubricant. To ensure your TRX2.5 racing engine is protected from internal corrosion, use thefollowing procedure:

1. Whenever possible, shut off the engine by pinching the fuelline closed. This allows most of the excess fuel to beconsumed by the engine. Be sure the throttle is in the idleposition. You may have to pinch the fuel line closed forseveral seconds before the engine stops.

2. Completely empty the fuel tank. Use your fuel-dispensingbottle to suck out the old fuel. Do not mix the old fuel withyour fresh fuel supply. If you leave fuel in the tank,transporting or handling your SportMaxx may cause fuel torun into the engine.

3. With the fuel tank empty and the throttle at the idleposition, try to start the engine. The engine will most likelystart and run for a few seconds as it uses up any fuelremaining in the engine and fuel lines.

4. Once the engine stops, clean the outside of the engine withcompressed air or spray motor cleaner. Once the engine isclean and dry, remove the glow plug power wire, glow plug,and air filter.

5. Open the throttle fully and spray a one-second burst ofWD-40 into the carburetor and into the glow plug hole(Caution! Wear safety glasses to prevent spray from gettinginto your eyes).

6. Place a rag or paper towel over the engine to catch anyWD-40 that may come out the carburetor or glow plug hole.

7. Connect the EZ-Start controller to the model and spin theengine for 10 seconds.

8. Remove the rag or paper towel and repeat steps 5–7 twomore times.

9. Clean and re-oil the air filter so it will be ready for use nexttime. See page 27 for air filter maintenance instructions.

10. Replace the glow plug, reconnect the glow plug power wire,and reinstall the air filter.

Denatured alcohol(available fromhome centers and

paint supply stores) in aspray bottle is an extremelyeffective cleaner. Be sure towear safety glasses andgloves when working withdenatured alcohol.

Fun fact: WD-40™

stands for “waterdisplacement

attempt #40.” The WD-40™

product used today was thesuccessful 40th attempt atcreating a water-displacinglubricant. WD-40™ was thelab test label.

Be sure to followproper maintenanceand storage

procedures to avoiddamage to your engine andother components of yourSportMaxx.

Don’t put the fuelfrom your tank backinto your fuel jug.

Dispose of it properly,following city or countyregulations.

Always wear eyeprotection whenusing compressed

air or spray cleaners andlubricants.

44

45

ABC 23After-run maintenance 21, 43, 44After-run procedure 44Air density 28, 35Air Filter 7, 22, 23, 27, 35, 43, 44

Cleaning 21, 27foam 23maintenance 42oil 6

Air Intake 22Air temperature 36, 42Air/fuel mixture 28Air/fuel ratio 28, 29, 32Airflow 36Ambient temperature 36Antenna (receiver) 11, 15, 41

tip 15tube 15wire 15

Antenna (transmitter) 11, 15, 41Antenna Mount 7Atmospheric conditions 28, 36, 42Axle pins 9Barometric pressure 35, 42Baseline setting 35Batteries 6, 12, 13, 14, 41

charging 30receiver 13, 14rechargeable 13, 14transmitter 13

Batteries, Ni-MH (nickel-metalhydride) 13Batteries, NiCad (nickel-cadmium)6, 12, 13, 30Battery box 7Battery compartment (Transmitter)11, 13Battery holder 11, 14Bearings 44Big Block .15 23Binding 42Body mount 7Brake 19

Bulkhead 7Bumper 7Bumper mount 7CA glue 9Camber 38Carb, see also Carburetor 23Carburetor 22, 23, 28, 42

adjustments 28barrel 23fine-tuning 35slide 25venturi 28

Caster 39Channel 11, 12, 17, 18Channel number 12Charger 6, 30

peak-detecting 30timed 30

Chassis 7Clean-out 23Cleaning 43Clearing your frequency 12Clutch bell 22Combustion 28Combustion chamber 23Compression 24, 42, 43Connecting rod 23, 43Cooling fins 23Crankcase 22, 23Crankshaft 22, 23, 44Cross-brace 7Crystal 12, 18

Access Plug 7Curbs 37Customer service 4, 41Cylinder sealing 32Decals 10Differential 7Drivetrain friction 37Driving Tips 37Dyno 23E-mail 4Engagement pawls 41

Engine, TRX 2.5 7, 22, 26"cutting out" 34break-in 21, 23, 32

driving procedure 33cooling 36, 43damage 27detonation 34failure 27, 43flooding 31, 41, 42hesitation 34life 42, 43maintenance 43mount 22overheating 34performance 29priming 25, 32, 42revving 37shut off 44sluggish acceleration 34stalling 25, 32, 34, 42, 43temperature 34, 36terms 23tuning 28, 34

by temperature 36Exhaust 5, 22Exhaust fumes 32EZ-Start 6, 23, 24, 30, 41

“glow plug” LED 30, 31, 41“motor” LED 30, 31, 41battery 30, 41controller 22, 31, 41, 42, 44cush drive 30drive unit 22motor 7, 22, 31, 41plug 7, 22Protection Mode 31, 41Smart Start™ 30, 31

Fit 23Flag color 12Flame-out 24Flooding, see Engine; floodingFlywheel 22, 41Frequency band 12, 15

Fuel 5, 6, 24, 26, 42, 44break-in fuel 32fuel dispensing bottle 6, 26

Traxxas Top Fueler 26Traxxas Top Fuel 24, 26, 42unburned 44

Fuel flow 28Fuel intake 22Fuel line (fuel tubing) 7, 22, 24, 42Fuel mixture adjustment 35

high-speed fuel mixture 34low-speed mixture 35

Fuel mixture, see also air/fuelmixture 24, 34, 35, 42Fuel tank 7, 22, 26, 44

emptying 44filling 26fuel level 32tank lid 7, 26tank seal 26

Glow plug 24, 30, 31, 32, 34, 41-42driver 24fouled 32igniter 30power wire 22, 42, 44

Ground wire 22Half shaft 7Head (cylinder head) 22, 23Head Protector 22Header 7, 24Hex hubs 9Humidity 35Idle adjustment screw 35Idle speed 17, 24, 29, 32, 33, 34, 35Idle Speed Adjustment 29, 33, 35Idle Speed Screw 22, 24, 29Jumping 37Lean 24, 29

leaning the mixture 24maximum safe lean setting 34-35,36

Lubrication 29Maintenance 43

Index

Maintenance schedule 21Methanol 44Mixture needles 34

high-speed needle 22, 24, 28, 35, 42low-speed needle 22, 24, 28, 35

Moisture 43, 44Needle seat 28Needle settings 42Needle valve 24Negative wire 22Neutral (center) point 16-17Neutral position 12Nitro 24

content 24, 26percentage 26

compensating for 35Nitromethane, see also Nitro 24O-ring 24Oil 6

after-run 6, 44filter 6WD-40™ 6, 44

Oil Dampers, see ShocksOn/Off switch 7, 11, 14, 18, 41Over revving 37Peak detection, see ChargerPinch test 35Pipe (tuned) 7, 22, 24, 25Pipe hanger 7Piston 24, 32

wrist pin 43, 44Piston and Sleeve 42, 43Pivot balls 38Port 24Positive Wire 22Power Switch 11Pressure Line 7, 22Priming, see Engine; primingProGraphix 10Punch 25Quick Start 8, 9, 10, 13, 14, 15, 18,19, 20, 26, 30, 31, 32, 34, 37, 43Radio interference 5, 20

Radio System 11, 12, 19, 41adjustments 16controls 16range-testing 20rules 18terminology 12terms 12

Range 14, 15, 18, 20, 41short 41

Receiver 11, 12, 41cover (box) 7, 15, 41

Required equipment 6Rich 25, 29Ride height 39, 40Rollovers 37RPM 25

limits 37Safety 5Servo reversing switches 11, 16Servos 7, 11, 12

reversing 11, 17steering 7, 11, 17, 19throttle/brake 7, 11, 16-17, 19

Shipping 4Shock Mounting Positions 39, 40

Lower 39Upper 40

Shock progression 39Shock Tower 7Shocks 7, 38

Fine Tuning 38Shuddering 41Skid Plate 7Sleeve 25, 32Slipper Clutch 7, 38, 43

adjusting 38pegs 43

Smoke 34Spring rate 40Spur Gear 7Stalling, see Engine; stallingStarter shaft 44Starting, see Engine; starting

Steering mechanism 19Steering Trim, Electronic 11, 12, 17,19Steering Wheel 11, 19Storage 44Supplies 6Support 4, 41Suspension

adjusting 39, 40Suspension Arms 7Tank 1 33Tank 2 33Tank 3 33Tank 4 33Tank 5 33Tank 6 33Temperature, see Engine;temperatureTemperature gauge 36

digital temperature gauge 36infrared temperature probe 36

Throttle Arm 22Throttle Neutral Adjustment 11, 16Throttle response 35Throttle slide 35Throttle Trigger 11, 16, 19Throttle Trim, Electronic 11, 12, 16,19, 35Toe-in 38Tools 6TQ-3, see also Radio System 11Transmission 7Transmitter 12, 18, 41

indicator light 19power indicator 11, 13

Traxxas Lifetime EngineReplacement Plan 43Trim, see also Throttle Trim and Steering Trim 12Troubleshooting 41Turnbuckle 7Turns 37, 39Understeer 39

Water 42Wear-in 25Weather conditions 35Wheelies 34Wheels 9Wiring diagram 11WOT 25, 28X-tal see also Crystal 12Zero-scrub-radius 19

46

Index

SportMaxxOwner’s Manual

Model5110

Traxxas Corporation, 1100 Klein Road, Plano, Texas 75074, Phone: 972.613.3300, Toll-free 1-888-TRAXXASTraxxas U.K., P.O. Box 1128, Winterbourne, Bristol BS17-2SH, England, Phone: 44.117.956.1002

Internet: www.Traxxas.com, www.T-Maxx.com

Documents

TRX 2.5 Illustrated...The TRX 2.5 Racing Engine Flame-out - Occurs when the engine stops running at high RPM. Usually the fault of an excessively lean fuel mixture or glow plug failure