pulled completely away from the needle seat leaving it fully
open. At that point, fuel metering is entirely controlled by the
high-speed needle. Again, using our water hose example, when
the spray nozzle at the end of our garden hose is fully open,
then the main water valve can be used to adjust how fast the
water flows.
The engine’s performance is directly linked to the fuel
mixture. Richening the fuel mixture increases the amount of
fuel in the air/fuel mixture ratio and leaning the fuel mixture
decreases the amount of fuel in the air/fuel mixture ratio.
Slightly lean fuel mixtures deliver stronger, more efficient
combustion and more power, but with less lubrication.
Slightly rich fuel mixtures deliver cooler running and more
lubrication but with slightly less power.
Tuning the engine means finding the perfect balance between
the two; excellent power to meet your needs while maintaining
good lubrication for long engine life.
The optimal fuel mixture
setting is rich
to provide a safety margin against having a lean
condition if some variable changes (such as the temperature
from one day to the next).
General fuel mixture settings are measured by the number of
turns the needles are turned out from fully closed. The fuel
mixture settings have been pre-set from the factory to typical
break-in settings. Do not readjust your carburetor from the
factory settings until after the engine is started and running,
and you have been able to observe the engine running to
assess what minor adjustments may be required to compensate
for fuel, temperature, and altitude. Adjustments are usually
made in 1/8 or 1/16-turn increments.
The Idle Speed Adjustment
The idle speed screw controls the closed position of the throttle
slide. When the throttle servo is in its neutral position, the
throttle slide should be stopped against the idle adjustment
screw. Always use the idle speed adjusting screw to control
engine idle. Do not use the throttle trim on the transmitter to
adjust idle speed. The idle speed should be set as low as
possible and still maintain reliable running.
▼▼
The TRX 2.5 Racing Engine
Water Valve
(Controls Overall Flow)
High Speed Needle
Water Nozzle
(Controls Fine Flow)
Low Speed Needle
See
Tuning the TRX 2.5
for Best Performance
on page 34 for
complete information on
adjusting the air/fuel
mixture and idle speed.
29
Lean
Rich
TRX 2.5 Factory
Needle Settings
If your factory preset
carburetor adjustments
have been tampered with,
use the following settings:
• Set the high-speed needle
to 4 turns out from closed.
• Set the low-speed needle
so the screw head (
red in
Fig. A
) is flush (even) with
the end of the slide (
yellow
in Fig. A
).
Always use the factory
settings for initial starting.
Only use these settings
when the factory settings
have been lost.
Low Speed
Needle Adjustment
Fig. A
