Traxxas TRX 2.5R Owner'S Manual Download Page 25 | Manualshive

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TRX 2.5R • 25

2.

If necessary, remove the air filter to gain access to the idle adjustment screw.

3.

Turn the screw counterclockwise to reduce the idle speed, or clockwise to increase it.
The idle speed should be set as low as possible while still maintaining reliable
running characteristics.

4.

Reset the throttle trim on the transmitter to its original position.

Fine-Tuning the Carburetor

After fine-tuning your TRX 2.5R Racing Engine at the end of the break-in procedure, no major
adjustments to the fuel mixture are usually necessary. Make note of the temperature, humidity,
and barometric pressure at the time you finished fine tuning your carburetor. Current weather
conditions can be found online from national websites, local TV news websites, and television.
This information will be considered your baseline setting. You may need to adjust your
carburetor needles to compensate for changes in temperature and barometric pressure (air
density) from day to day. Generally, you’ll need to richen the fuel mixture when the weather is
colder than your baseline temperature and the air density is higher. Lean the fuel mixture when
weather is warmer than your baseline temperature and the air density is lower. The chart below
provides general guidelines on how weather conditions affect air density when they move
higher or lower than your baseline setting (see page 14 for detailed info on how air density
affects mixture settings).

If the...

Humidity

Pressure (barometer)

Temperature

Altitude

Nitro %

is..

Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher

then the

air density is...

Slightly more dense
Slightly less dense

Less dense
More dense
More dense
Less dense
More dense
Less dense

adjust (correct)

the fuel mixture to be...

Slightly richer
Slightly leaner

Leaner
Richer
Richer
Leaner
Richer
Leaner
Leaner
Richer

TUNING THE TRX 2.5R

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Summary of Contents for TRX 2.5R

Page 1: ...OWNERS MANUAL ...

Page 2: ...d trademarks of Traxxas Other brand names and marks are the property of their respective holders and are used only for purposes of identification No part of this manual may be reproduced or distributed in print or electronic media without the express written permission of Traxxas Note Some photos show the engine equipped with optional accessories such as the EZ Start system headers and engine moun...

Page 3: ...any questions about your TRX 2 5R Racing Engine or its operation call the Traxxas Technical Support line toll free at 1 888 TRAXXAS 1 888 872 9927 Technical support is available Monday through Friday from 8 30am to 9 00pm Central time Technical assistance is also available at www Traxxas com You may also e mail customer support with your question at support Traxxas com Join thousands of Traxxas R ...

Page 4: ...n a fuel dispensing bottle may look like a cool drink to a child Keep all fuel out of the reach of children at all times Do not place fuel containers on the ground where children can get to them while you are driving R C fuel is flammable Never allow smoking sparks heat or flame in the presence of fuel or fuel vapors The engine and exhaust system may become extremely hot during use Be careful not ...

Page 5: ...w the new break in procedure as closely as possible to achieve the best performance and longest life from your TRX 2 5R Racing Engine Old style break in procedures such as simply running the engine with a very rich fuel mixture for the first 4 tanks of fuel will not achieve the best results Follow the steps in this manual to successfully break in the TRX 2 5R Racing Engine A routine maintenance sc...

Page 6: ...ctor PowerTune Head Cylinder Head Pull Starter Low Speed Needle Throttle Arm Clutch Bell Flywheel Carburetor Air Intake Fuel Intake High Speed Needle Idle Speed Screw Crankshaft Crankcase Air Filter Housing TRX 2 5R Racing Engine Illustrated Optional Backplate ...

Page 7: ...ferent 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 of carburetors slide carbs and barrel carbs The TRX 2 5R uses the superior slide carburetor design Clean out Cleaning out is a condition that occurs when the engine is accelerati...

Page 8: ...n and sleeve If the fit is tight the piston will feel very tight at top of the sleeve and the engine will have good sealing and compression If the fit is loose compression will be low and both the piston and sleeve should be replaced Flame out Occurs when the engine stops running at high RPM Usually the fault of an excessively lean fuel mixture or glow plug failure Fuel 10 20 The TRX 2 5R must hav...

Page 9: ...ves Low speed needle LSN Needle valve that controls the low speed fuel mixture Needle valve Valve consisting of a tapered needle that closes against a corresponding seat to regulate fuel flow Nitro Abbreviation for nitromethane a component of model engine fuel that improves fuel combustion and power output Nitro also refers to a class of R C powered by model engines instead of electric Nitro conte...

Page 10: ...unburned fuel coming from the exhaust RPM Abbreviation for revolutions per minute how many times the engine crankshaft spins in a minute Sleeve Internal engine part that contains the piston The precise fit between the sleeve and the piston creates a seal that allows engine to have the required compression for combustion The sleeve in a TRX engine is made of brass and is then hard chrome plated Sli...

Page 11: ... to match the metallurgy and temperature characteristics of Traxxas engines You may use 10 or 20 nitro content fuel Use the same percentage all the time don t switch back and forth between 10 and 20 fuel If you break in your engine on 20 fuel then always use 20 fuel What About Other Fuels Can other brands of fuel be used besides Top Fuel There are other fuels that can provide satisfactory performa...

Page 12: ...rformance while protecting your engine from dust and dirt Use only the supplied filter You will not improve engine performance by switching to an aftermarket filter and you may risk engine damage due to poor filtration The TRX 2 5R air filter assembly consists of 3 pieces 1 A rubber filter base 2 A plastic housing consisting of a permanently assembled mesh cap and body 3 An oiled foam element You ...

Page 13: ...ngines This type of filter oil is available at motorcycle pro shops Apply 30 drops of the Traxxas filter oil evenly to the top bottom and sides of the filter element 30 total drops divided among the 3 surfaces Squeeze the filter element repeatedly to help spread the oil throughout The filter element should be evenly colored by the oil Even color indicates that the oil is distributed evenly Do not ...

Page 14: ...tio remains roughly constant Due to variations in atmospheric conditions temperature humidity altitude etc fuel flow adjustment valves called fuel mixture needles are required to meter the fuel and maintain the ideal air fuel ratio in these ever changing conditions For example colder air is more dense more air molecules for a given volume of air and therefore requires more fuel more fuel molecules...

Page 15: ...elerate from idle the throttle opens and the low speed needle is pulled away from the needle seat This allows more fuel to flow with the increased air flow As the throttle is increased the low speed needle is pulled completely away from the needle seat leaving it fully open At that point fuel metering is entirely controlled by the high speed needle Again using our water hose example when the spray...

Page 16: ... Do not readjust your carburetor from the factory settings until after the engine is started and running and you have been able to observe the engine running to assess what minor adjustments may be required to compensate for fuel temperature and altitude Adjustments are usually made in 1 8 or 1 16 turn increments The Idle Speed Adjustment The idle speed screw controls the closed position of the th...

Page 17: ... disappear once your engine is fully broken in Many owners report not experiencing any of these symptoms with the TRX 2 5R Racing Engine We recommend replacing the glow plug with a new one after the engine break in procedure Engine Break in Procedure The focus during break in is to vary and limit the engine speed This will be accomplished by accelerating and stopping at different rates for the fir...

Page 18: ... start your TRX 2 5R Racing Engine for the first time make sure you have read all instructions and precautions in this manual Pay close attention to the tank by tank break in instructions in the next section and make sure you have read and understood them before you run your engine Your engine must be at room temperature 70 F or 21 C or above the first time you start it If it s cooler than room te...

Page 19: ...retor use the installed clamp 5 Let the engine cool for 15 minutes Note If at any point the engine cuts out or stalls during gentle acceleration richen the high speed needle 1 4 turn by turning the needle counterclockwise Tank 2 1 From tank 2 forward model should be driven with the body on 2 Driving procedure Gently pull the throttle trigger to about 1 2 throttle over a 2 second count Then gently ...

Page 20: ... count Then gently apply the brake to stop Count the three seconds out while accelerating one thousand one one thousand two one thousand three and then stop Repeat this starting and stopping procedure until the fourth tank of fuel is nearly empty 2 Apply the throttle gradually Your finger should not reach full throttle until the end of the three second count 3 Keep your driving smooth and consiste...

Page 21: ...warmer running conditions Warm the engine to approximately room temperature by removing all fuel and storing the vehicle inside at room temperature until just before starting the engine An extremely cold engine can become difficult to start After the engine is running it is important to keep the temperature of the engine to at least 200 to 215 degrees during break in In weather below 45 degrees th...

Page 22: ...r engine below 35 degrees Fahrenheit If you insist on running your vehicle below 35 degrees be aware that nitro engines may be very difficult to start and tune at those extremely cold temperatures Also at temperatures below freezing nitro fuel can actually begin to gel up and this can be harmful to the engine Follow the remaining break in procedures as outlined in this owner s manual This along wi...

Page 23: ... fuel mixture increases performance High Speed Fuel Mixture Adjustment With the engine warm and running at a rich setting gradually lean the high speed fuel mixture in 1 16 turn increments Make several high speed passes after each adjustment to clear out the engine and note any change in performance The TRX 2 5R is extremely powerful Remember to apply the throttle gradually to prevent wheelies or ...

Page 24: ...ly the engine s throttle response should be very quick Idle Speed Adjustment Once the high and low speed mixtures have been set reduce the idle speed to the minimum reliable idle speed Remember this adjustment should be made while the engine is running at normal operating temperature 1 Turn the throttle trim on the transmitter so that the brakes are applied This ensures that the throttle slide is ...

Page 25: ... You may need to adjust your carburetor needles to compensate for changes in temperature and barometric pressure air density from day to day Generally you ll need to richen the fuel mixture when the weather is colder than your baseline temperature and the air density is higher Lean the fuel mixture when weather is warmer than your baseline temperature and the air density is lower The chart below p...

Page 26: ...eventy degree weather For this reason we cannot give you a definitive temperature range that indicates the best possible engine tuning The temperature gauge can aid you in tuning by giving you a relative indication of how your adjustments are affecting the engine and by preventing you from exceeding maximum engine temperature For example as you lean the fuel mixture the engine performance will inc...

Page 27: ...Remove the fuel line where it connects to the carburetor to see if there is fuel in it If not you may need to prime the engine Reconnect the fuel line and then refer to page 18 for instructions on priming the engine Check your fuel mixture settings It may be necessary to adjust the fuel mixture if the outside temperature or barometric pressure has changed significantly since the last time the engi...

Page 28: ...an t always be accounted for with a single high speed needle setting The symptoms described above can occur when the air 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 and see if there is any improvement in starting and idling Lean the fuel mixture only until the engine will run and idle reli...

Page 29: ...e the glow plug and gasket with the glow plug wrench supplied with your model A 5 16 8mm nut driver will also work 2 Turn the model upside down 3 Pull the starter handle several times to clear the engine of excess fuel 4 Turn the model over and reinstall the glow plug and gasket 5 Do not prime the engine Apply 1 2 throttle and pull the starter The engine should start immediately Piston Stuck at To...

Page 30: ...osits This is extremely important for the life of the engine See page 31 for after run maintenance procedures Inspect the vehicle for obvious damage or wear Look for 1 Loose or missing screws 2 Cracked bent or damaged parts 3 Cut or loose wiring 4 Cut or kinked fuel lines 5 Signs of fuel leakage Inspect the gears for wear broken teeth or debris lodged between the teeth After run Procedure You must...

Page 31: ...ops clean the outside of the engine with compressed air or spray motor cleaner Once the engine is clean and dry remove the glow plug power wire glow plug and air filter 5 Open the throttle fully and spray a one second burst of WD 40 into the carburetor and into the glow plug hole Caution Wear safety glasses to prevent spray from getting into your eyes 6 Place a rag or paper towel over the engine t...

Page 32: ...o idle Replace the wrist pin and G clip whenever the piston and sleeve are replaced Follow the instructions for the proper break in procedure of a new TRX 2 5R Racing Engine whenever the piston and sleeve are replaced Connecting rod The connecting rod should be replaced when the piston and sleeve are replaced or after three gallons of fuel whichever comes first Also replace the piston wrist pin an...

Page 33: ... slide the 5x8x0 5TW with the clutch bell off of the crankshaft Nitro 4 Tec owners will need to slide two 5x8x0 5TW off the pilot shaft Caution It s important to use eye protection when removing the E clip from the shaft to prevent the clip from causing an injury Pull the clutch shoes off of the flywheel pins Remove the flywheel nut from the crankshaft using an 8mm socket 202 and disconnect the fl...

Page 34: ...slide up and out of the crankcase 402 Note If the sleeve does not slide out of the crankcase with reasonable effort slightly warm the crankcase with a hair dryer or heat gun to about 130 F The sleeve should slide out easily at this temperature Use gloves to protect against burns Rotate the crank to where the rod and piston are located at TDC top dead center top of the piston s stroke 403 Gently pu...

Page 35: ...he crank pin then the crank pin is worn and the crankshaft will need to be replaced Important Do not reuse a damaged or worn crankshaft This will dramatically shorten the life of your rebuilt engine If there are damaged or worn parts beyond the piston sleeve and connecting rod it may be best to take advantage of the Traxxas Engine Replacement Program 8 Slide the crankshaft back through the crank b...

Page 36: ... cooling head Slowly tighten each screw just a little at a time in a crossing pattern see picture 1003 until each bolt becomes snug Finish each bolt in the same pattern with 9 11in lbs of torque 9 Apply a drop of after run oil in the piston s wrist pin bore before installing the wrist pin Locate the oil hole refer to pic 901 in the connecting rod and the skirt relief side of the new piston Insert ...

Page 37: ... case 1201 Slide the flywheel over the pilot shaft and onto the split cone washer The split cone washer should fit inside of the tapered hole in the flywheel Thread the flywheel nut all the way up to the flywheel and tighten the flywheel with 55 65 in lbs of torque against the flywheel 1202 13 Slide the clutch shoes onto the flywheel Key the flywheel pins into the holes of the clutch shoes See pic...

Page 38: ...art onto the starter shaft that exits the backplate of the engine Line up the drive with the roller clutch Fasten the EZ Start gear case to the backplate with the three 3x12BCS screws 1502 Fasten the pull starter with 4 3x12BCS 16 Inspect the exhaust O ring and replace it if it is damaged or torn Fasten the exhaust header and pipe assembly back onto the rear of the engine case with the two 3x15CS ...

Page 39: ...Start 8 Fit 8 Flame out 8 Flywheel 6 Fuel 4 8 11 handling 12 intake 6 nitro content 11 other fuels 11 TraxxasTop Fuel 11 tubing 8 Fuel Mixture 8 15 atomization 14 high speed mixture see High Speed Adjustment lean 9 15 16 leaning 9 low speed mixture see Low Speed Adjustment ratio 14 rich 10 15 16 Glow plug 8 driver 9 Header 9 High Speed Adjustment 22 high speed needle 6 9 Idle Speed 9 16 23 idle sp...

Page 40: ...1 1 00 Klein Road Plano Texas 75074 1 888 TRAXXAS 051007 ...

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