Traxxas 4902, Owner'S Manual

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T-MAXX 2.5R
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Tuning Your TRX 2.5R Racing Engine
The engine’s performance depends on the fuel mixture. Turn the mixture
needles clockwise to lean the fuel mixture and counterclockwise to
richen it. Leaning the fuel mixture will increase engine power up to the
engine’s mechanical limits.
Never run the engine too lean (not enough
fuel flow). Never lean the engine until it begins to cut-out or stall.
Leaning the engine beyond the safe allowable limits will result in poor
performance and almost certain engine damage.
Indications of 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 and richen the
high speed mixture 1/4 turn. The engine will probably be slightly rich at
that setting and you can then retune for performance. Always tune for
performance by starting rich and moving leaner toward the ideal setting.
Never try to tune from the lean side. There should always be a light
stream of blue smoke coming from the exhaust.
Before you begin tuning, the engine should be warmed up to its normal
operating temperature and running slightly rich. All final tuning adjustments
must be made to the engine at its normal operating temperature. You can
tell the engine is running rich by noting any of the following:
Sluggish acceleration with blue smoke coming from the exhaust.
T-Maxx 2.5R may not shift into second gear.
There is unburned fuel spraying from the exhaust tip.
Leaning the high-speed 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 loss of control.
Continue this procedure until there is no longer any performance
improvement.
If any one of the following conditions occurs, the fuel
mixture is already past the maximum safe lean setting:
1. There is no longer any performance improvement.
2. 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 acceleration.
Popping or clattering sound when decelerating (detonation).
Fluctuating idle speed.
Temperature measurement above 270° F at the glow plug
(A temperature reading above 270° alone does not necessarily
indicate overheating. Look for other symptoms of overheating
combined with temperature for a more accurate warning).
Richen the fuel mixture to the optimum setting by richening the high-
speed needle at least 1/8 turn counterclockwise and retest. This setting
will extend engine component life.
When tuning for
performance, watch closely
to notice when there is no
longer any increase in speed
or power when the
high-speed mixture is lean.
If you lean the high-speed
mixture to the point that the
engine cuts-out, hesitates,
or stalls, you are well into
the danger zone and engine
damage is likely. Richen the
high-speed needle 1/4 turn
and retune.
For your convenience, the
low-speed needle has a
positive stop that prevents
it from being over tightened
and damaging the needle
and seat. This also provides
an easy way to gauge how
many turns out from closed
the low-speed needle
adjustment is set to.
The TRX 2.5R Racing Engine