Idle Speed Adjustment; Fine-Tuning The Carburetor - Traxxas Jato 3.3 5507 Owner's Manual

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
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 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
THE TRX 3.3 RACING 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 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 body, windshield, and front
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 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.
JATO 3.3 • 27