T-MAXX 3.3 OWNER’S MANUAL • 21
THE TRX 3.3 RACING ENGINE
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 the brakes are
applied (note its original position). This ensures that the throttle
slide is resting against the idle 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.
3. Reset the throttle trim on the transmitter to its original position.
Fine-Tuning the Carburetor
After fine-tuning your TRX 3.3 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 15 for detailed info on how air
density affects mixture settings).
Tuning the Engine by Temperature
Your model is equipped with a temperature sensor to
indicate the engine’s temperature on the dashboard
of the Traxxas Link application (available separately,
see page 29). Engine temperature can be used as
an effective tuning aid when you understand the
relationship between engine temperature and ambient temperature. The
engine operating temperature, when tuned for maximum performance, will
vary according to atmospheric conditions, engine load, gauge accuracy, and
many other factors. The atmospheric condition that has the most influence
on engine temperature is air temperature. Expect the engine temperature
to vary almost in direct proportion to air temperature. Assuming you tuned
the engine for the same maximum performance each day, the engine will
run about twenty degrees hotter when it’s ninety degrees outside than it
would in seventy-degree weather. For this reason, we cannot give you a
definitive temperature range that indicates the best possible engine tuning.
The Traxxas Link application’s dashboard temperature gauge can aid you
in tuning by giving you a relative indication of how your adjustments are
affecting the engine and to help prevent you from reaching excessive
engine temperatures. For example, as you lean the fuel mixture, the engine
performance will increase along with the temperature. If you continue to lean
the fuel mixture and the temperature increases but the engine performance
does not change, then you have exceeded the maximum safe lean setting.
Make note of the engine temperature. Generally, try to keep your engine
from exceeding 270°F when measured at the glow plug. If necessary, increase
airflow to the engine by cutting out the rear of the windshield. In some
situations, the engine may perform very well with no stalling, lagging, or
hesitation at temperatures above 270°F, particularly in very hot climates.
If richening the fuel mixture to bring the temperature down to 270°F results in
poor, sluggish performance (engine never cleans out) then return the engine
back to a satisfactory state of tune based on how it sounds and performs
(always with a visible stream of blue smoke coming from the exhaust)-. If
engine temperature is exceeding 270°F with proper cooling and no signs
of abnormal running, then avoid running the engine at its maximum lean
setting. Watch closely for
any
signs of overheating.
Richen the fuel mixture slightly to provide a safety margin of additional
cooling lubrication. 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.
Fuel Mixture Adjustment Chart
If the...
is..
then the air
density is...
adjust (correct) the
fuel mixture to be...
Humidity
Lower
Slightly
more dense
Slightly richer
Higher
Slightly
less dense
Slightly leaner
Pressure
(barometer)
Lower
Less dense
Leaner
Higher
More dense
Richer
Temperature
Lower
More dense
Richer
Higher
Less dense
Leaner
Altitude
Lower
More dense
Richer
Higher
Less dense
Leaner
Nitro %
Lower
-
Leaner
Higher
-
Richer
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 14 for more information
There is NO optimal temperature that can be used as a target to
deliver the best engine tuning. Do not rely on a temp gauge alone
to tune your engine. Tune the engine by paying very close attention
to how it responds to changes in fuel mixture (more smoke/less
smoke, fast/sluggish, reliable/stalling, smooth sound/ muffled
sound, etc)
. Once the engine is tuned, then observe the temperature.
