Traxxas 55077-1 - Manual (Page 27)

JATO 3.3 • 27
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 20 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 39). 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.
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.
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.