NITRO RUSTLER • 27
ThE TRx 2.5 RacING ENGINE
15
TUNING YOUR TRx 2.5 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 re-tune 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.
• 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 2.5 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 re-tune.
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.
