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The TRX 2.5 Racing Engine
35
Low-Speed Fuel Mixture Adjustment
The low-speed mixture is always set after the high-speed needle
is correctly adjusted.The low-speed mixture will be 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.The engine should run for 2-3 seconds, speed
up, and then die.
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 dies 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, possibly even to the point of
making it difficult to keep the T-Maxx from doing a wheelie
when you accelerate!
Idle Speed Adjustment
Once the high and low-speed mixtures have been set, reduce
the idle speed to the minimum reliable idle speed.Remember,
this adjustment should be made while the engine is running at
normal operating temperature.
1. Turn the throttle trim on the transmitter so that the brakes
are applied.This ensures that the throttle slide is resting
against the idle adjustment screw.
2.
If necessary, remove the air filter to gain access to the idle
adjustment screw.
3.
Turn the screw counterclockwise to reduce the idle
speed,or clockwise to increase it.The idle speed should
be set as low as possible while still maintaining reliable
running characteristics.
4.
Reset the throttle trim on the transmitter
Note: If the idle speed is set too high it could prevent the T-Maxx
from shifting between forward and reverse.If you experience this,
simply reduce the idle speed.
Fine-Tuning the Carburetor
After fine-tuning your TRX 2.5 engine at the end of the break-in
procedure, no major adjustments to the fuel mixture are usually
necessary. Make note of the temperature, humidity, and
barometric pressure at the time you finished fine tuning your
carburetor. Current weather conditions can be found online
from national websites, local TV news websites, and Television.
This information will be considered your baseline setting.
You may need to adjust your carburetor needles to compensate
for changes in temperature and barometric pressure (air
density) from day to day. Generally,you’ll need to richen the fuel
mixture when the weather is colder than your baseline
temperature and the air density is higher. Lean the fuel mixture
when weather is warmer than your baseline temperature and
the air density is lower.The chart below provides general
guidelines on how weather conditions affect air density when
they move higher or lower than your baseline setting (see page
28 for detailed info on how air density affects mixture settings).
If the...
Humidity
Pressure (barometer)
Temperature
Altitude
Nitro %
is..
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
then the air density is...
Slightly more dense
Slightly less dense
Less dense
More dense
More dense
Less dense
More dense
Less dense
adjust (correct) the fuel mixture to be...
Slightly richer
Slightly leaner
Leaner
Richer
Richer
Leaner
Richer
Leaner
Leaner
Richer