10
Leaner
Richer
1 H
our
2 H
our
Low-Speed Adjustment
The low-speed adjustment affects the idle and slightly-off-idle
performance. The optimum setting allows the motor to idle
for at least 8−10 seconds. The model should then accelerate
with a slight amount of sluggishness and a noticeable amount
of smoke. The simplest way to check this is to make sure the
engine has been warmed up and let the engine idle for 8−10
seconds. If the low-speed mixture is so far off that the engine
won’t stay running that long, turn the idle stop screw clockwise,
increasing the idle speed. With the engine at idle, pinch and
hold the fuel line near the carburetor, cutting off the flow of
fuel, and listen closely to the engine rpm (speed). If the low-
speed needle is set correctly, the engine speed will increase
only slightly and then die. If the engine increases several
hundred rpm before stopping, the low-speed needle is too rich.
Lean the mixture by turning the needle clockwise one hour and
trying again. If the engine speed does not increase but simply
dies, the needle is too lean and needs to be richened up by
turning the needle counterclockwise one hour before trying
again. After you have optimized the low-speed setting, the
engine will probably be idling faster. You will have to adjust the
idle stop screw counterclockwise to slow the engine idle speed
down. The engine should accelerate at a constant pace without
hesitating.
Base Start-up Settings from the Factory
High-Speed Needle—2
1
/
2
turns out from bottom
Low-Speed Needle—2
1
/
2
turns out from bottom
Faster
Slower
Engine Tuning
After the engine is broken in, you can tune it for optimum
performance. When tuning, it is critical that you be cautious of
overheating as severe damage and premature wear can occur.
You want to make all carburetor adjustments in “one hour”
increments.
Leaner
Richer
3
1
2
1= Idle Stop Screw
2=Low-Speed Needle
3=High-Speed Needle
Carb Adjustments:
Make all carburetor
adjustments in one-hour
increments.
Imagine the slot in the
needle is the hour hand on
a clock. Adjust it as though
you were moving the hour
hand from one hour to the
next or previous one.