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The TRX 2.5 Racing Engine
Tuning the TRX 2.5 for Best Performance
When adjusting the
low-speed fuel
The engine's performance depends on the fuel mixture. Turn the
mixture, it is very
mixture needles clockwise to lean the fuel mixture and
important to make several
counterclockwise to richen it. Leaning the fuel mixture will
high-speed runs with the
increase engine power up to the engine's mechanical limits.
Nitro 4-Tec between
Never run the engine too lean (not enough fuel flow). Never
adjustments to clear out any
lean the engine until it begins to cut-out or stall. Leaning the
excess fuel. Perform the
engine beyond the safe allowable limits will result in poor
pinch test immediately after.
performance and almost certain engine damage. Indications
If the engine is allowed to
idle for a long period of time,
of an overly lean mixture include:
it could "load up" with fuel
and give you an inaccurate
measurement from your
pinch test.
If any of these conditions are present, stop immediately and
richen the high speed mixture 1/4 turn. The engine will
For your
probably be slightly rich at that setting and you can then retune
convenience, the
low-speed needle
for performance. Always tune for performance by starting rich
has a positive stop that
and moving leaner toward the ideal setting. Never try to tune
prevents it from being over
from the lean side. There should always be a light stream of blue
tightened and damaging the
smoke coming from the exhaust.
needle and seat. This also
provides an easy way to
Before you begin tuning, the engine should be warmed up to its
gauge how many turns out
normal operating temperature and running slightly rich. All final
from closed the low-speed
tuning adjustments must be made to the engine at its normal
needle adjustment is set to.
operating temperature. You can tell the engine is running rich
by noting any of the following:
When tuning for
performance, watch
closely to notice
when there is no longer any
increase in speed or power
when the high-speed
High-Speed Fuel Mixture Adjustment
mixture is lean. If you lean
With the engine warm and running at a rich setting, gradually
the high-speed mixture to
lean the high-speed fuel mixture in 1/16 turn increments. Make
the point that the engine
several high-speed passes with the Nitro 4-Tec after each
cuts-out, hesitates, or stalls,
adjustment to clear out the engine and note any change in
you are well into the danger
zone and engine damage is
performance. The TRX-2.5 is extremely powerful. Remember to
likely. Richen the high-speed
apply the throttle gradually to prevent loss of control. Continue
needle 1/4 turn and retune.
34
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.
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
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. The engine begins to cut out at high speed (Danger!)
2. There is a sudden loss of power during acceleration (Danger!)
3. 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
Richen the high-speed needle at least 1/4 turn counterclockwise
and retune for performance.
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