Traxxas T-Maxx 3.3 4907 Owner's Manual page 21

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.
Fuel Mixture Adjustment Chart
then the air
If the... is.. density is...
Slightly
Humidity Lower
more dense
Slightly
Higher
less dense
Pressure
Lower Less dense
(barometer)
Higher More dense
Temperature
Lower More dense
Higher Less dense
Altitude
Lower More dense
Higher Less dense
Nitro %
Lower -
Higher -
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
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
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
adjust (correct) the
twenty degrees hotter when it's ninety degrees outside than it would in
fuel mixture to be...
seventy-degree weather. For this reason, we cannot give you a definitive
temperature range that indicates the best possible engine tuning.
Slightly richer
There is NO optimal temperature that can be used as a target to
Slightly leaner
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
Leaner 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.
Richer
The temperature gauge can aid you in tuning by giving you a relative
Richer
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
Leaner
with the temperature. If you continue to lean the fuel mixture and the
temperature increases but the engine performance does not change,
Richer
then you have exceeded the maximum safe lean setting. Make note of the
engine temperature. Generally, try to keep your engine from exceeding
Leaner
270°F when measured at the glow plug. If necessary, increase airflow
to the engine by cutting out the rear of the body, windshield, and front
Leaner
valance. 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
Richer
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.
THE TRX 3.3 RACING ENGINE
The following procedures require an optional
infrared temperature probe or on-board
temperature gauge (Traxxas on-board digital
temperature gauge, part #4091). Engine
temperature can be used as an effective
tuning aid when you understand the
relationship between engine temperature
T-MAXX 3.3 OWNERS MANUAL • 21