Traxxas 4902, Owner'S Manual

T-MAXX 2.5R

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The engine could be worn. If the fit between the piston and sleeve is
loose, compression is reduced and the engine will be difficult to start
when it is warm, and may tend to stall when running and when the
throttle is closed suddenly to idle. Engine life depends on many factors
including fuel type, air filter maintenance, needle settings, and how the
engine was used. For example, if the engine was allowed to ingest dirt
from lack of air filter maintenance or running through water, then the
internal engine components could wear out extremely fast.

Glow plug may have failed. If using an EZ-Start, check to see if the glow
plug light is on during starting. If not, replace the glow plug. If using a
glow ignitor, remove and check the glow plug.

Engine performance sluggish:

Engine performance depends mostly on the fuel mixture settings 
and how they compensate for the current atmospheric conditions.
Before you suspect other failures with the engine, richen the high-speed
needle at least 1/4 turn and then retune the engine for performance (see
page 31).

If the fuel mixture seems to be set correctly, make sure the fuel is fresh. If
the fuel is old, or was left uncapped for a long period, then some of the
important fuel components could have evaporated. Try new, fresh,
Traxxas Top Fuel.

Try a new Traxxas glow plug. Sometimes a glow plug will work well
enough to start the engine but not be able to deliver the engine’s full
performance potential.

Check to make sure there is no binding in the driveline that would cause
excessive loads on the engine.

Clearing a Flooded Engine

If the engine is primed for too long during startup, then it can become
flooded with fuel. When the engine is flooded it will no longer turn due to
excess fuel in the combustion chamber preventing upward movement of
the piston. Use the following procedure to clear a flooded engine:

1.

Remove the blue glow plug wire.

2.

Remove the glow plug and gasket with the glow plug wrench supplied
with your model. A 5/16 or 8mm nut driver will also work.

3.

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

4. 

Push the EZ-Start button for several seconds to clear the engine 
of excess fuel. Do not look into the glow plug hole while the 
engine is spinning or you could spray fuel into your face!

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 and push 
the EZ-Start button. The engine should start immediately.

Piston stuck at “top dead center” (TDC)

“Top dead center” is the position where the piston is at the very top of the
tapered sleeve. Occasionally an engine can get “stuck” at this position. This
is most likely to happen on new engines during break-in, but can also
happen at other times. If the engine is stuck at
TDC, use the following procedure to release the
piston from the sleeve:

1. 

Remove the glow plug using the included tool
or 8mm (5/16") nut driver and verify that the
piston is at the top of its stroke.

2. 

Use a flat blade screwdriver to rotate the
flywheel. Place the blade of the driver into one
of the grooves of the flywheel and push down,
turning the flywheel counter-clockwise when
viewed from the front. The flywheel should
turn, unsticking the piston from the sleeve.

3. 

Put two or three drops of light machine oil into
the glow plug hole to lubricate the piston and
sleeve. Do not use too much oil. It will hydro-
lock the engine. Verify the starter will spin the
engine with the glow plug out.

4. 

Rotate the flywheel so the piston is at bottom
dead center and replace the glow plug with
gasket. Reconnect the blue glow plug wire.

5. 

You should now be able to start 
the engine with the EZ-Start.

Top Dead Center

Bottom Dead Center

Troubleshooting Your T-Maxx 2.5R