28 • NITRO RUSTLER
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 Nitro Rustler 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. Always use the idle speed adjustment screw to control
engine idle.
1. When the throttle servo is in its neutral position, the throttle slide
should be stopped against the idle speed adjustment screw.
2. 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.
When adjusting the low-
speed fuel mixture, it is very
important to make several
high-speed runs with Nitro
Rustler 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.
Higher nitro requires a richer
fuel mixture. When running
33% fuel, richen your high-
speed needle 3/4 turn if
previously running 20% nitro
and then re-tune the engine
for maximum performance.
See page 18 for more
information.
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
If the...
Humidity
Pressure (barometer)
Temperature
Altitude
Nitro %
Fuel Mixture Adjustment Chart
ThE TRx 2.5 RacING ENGINE
