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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.
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.
If the...
Humidity
Pressure (barometer)
Temperature
Altitude
Nitro %
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
Fine-Tuning the Carburetor
After fine-tuning your TRX 2.5 racing 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).
is..
then the air density is...
Lower
Slightly more dense
Higher
Slightly less dense
Lower
Less dense
Higher
More dense
Lower
More dense
Higher
Less dense
Lower
More dense
Higher
Less dense
Lower
Higher
The TRX 2.5 Racing Engine
adjust (correct) the fuel mixture to be...
Slightly richer
Slightly leaner
Leaner
Richer
Richer
Leaner
Richer
Leaner
Leaner
Richer
Check the Traxxas
website for additional
information on base
line settings for your area.
35
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