Traxxas T-Maxx 3.3 4907 Owner's Manual page 20

THE TRX 3.3 RACING ENGINE
TUNING YOUR TRX 3.3 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.
the engine too lean (not enough fuel flow). Never lean the engine
until it begins to cut-out or stall.
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 3.3 may not shift into second gear.
• There is unburned fuel spraying from the exhaust tip.
• Leaning the high-speed fuel mixture increases performance.
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.
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 3.3 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.
20 • T-MAXX 3.3 OWNERS MANUAL
Never run
Leaning the engine beyond the safe
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.
Low-Speed Fuel Mixture Adjustment
The low-speed mixture is always set after the high-speed needle is
correctly adjusted. The low-speed mixture is set using the "pinch test".
1. Once the engine is warm, do several high-speed runs to confirm
that the high-speed needle is set correctly.
2. Bring the vehicle in and pinch closed the fuel line going into the
carburetor (use the engine shut-off clamp). The engine should run for
2-3 seconds, speed up, and then shut off.
3. If the engine runs longer than 3 seconds, then lean the low-speed
needle 1/16 turn, make several more high-speed runs, and retest.
4. If the engine shuts off immediately without speeding up, then richen
the low-speed needle 1/8 turn, make several more high-speed runs,
and retest.
When the low-speed needle is set correctly, the engine's throttle
response should be very quick, even to the point of making it difficult to
keep T-Maxx 3.3 from doing a wheelie when you accelerate!
When adjusting the low speed fuel mixture, it is very important to
make several high-speed runs with T-Maxx 3.3 between adjustments
to clear out any excess fuel. Perform the pinch test immediately
after. If the engine is allowed to idle for a long period of time, it could
"load up" with fuel and give you an inaccurate measurement from
your pinch test.