Losi LST XXL User Manual - Manual (Page 4)

Page 4
Base Start-up Settings from the Factory
High-Speed Needle—2 3 /
4
turns out from bottom
Low-Speed Needle—2 1 /
2
turns out from bottom
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.
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.
Hi-Speed Adjustment
After initial acceleration, the engine should pull at a steady rate while maintaining a two-stroke whine and a
noticeable trail of smoke. If the engine labors and is sluggish with heavy smoke, the mixture is too rich and needs
to be leaned by turning the high-speed needle clockwise in one-hour increments until it runs smoothly. If the
engine isn’t smoking or starts to die after acceleration, it is too lean and you must richen the mixture by turning
the needle counterclockwise. Don’t be confused by the sound of the engine and the actual performance. A
leaner mixture will produce an exhaust note with a higher pitch but this does not necessarily mean improved
performance, as the engine is on the verge of overheating and may incur possible damage. Ideally you want to
run the engine so that it is on the slightly rich side of optimum. This will give you the best combination of speed
and engine life. CAUTION: The engine is too lean and overheating if it accelerates rapidly with a high-pitched
scream then seems to labor, stops smoking, or loses speed. This can be caused by the terrain, atmospheric
conditions, or drastic altitude changes. To avoid permanent engine damage, immediately richen the mixture by
turning the high-speed needle counterclockwise at least “two hours” and be prepared for further adjustments
before running any more. Note: The normal operating temperature as seen on your radio screen should be in the
190 to 220° F (88 to 105° C) range.
1 H
our
2 H
our
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.
High-Speed Needle
As you turn this clockwise (leaner),
less fuel enters the engine.
Turning it counterclockwise
(richer) allows more fuel to enter
the engine.
Idle Speed Screw
As you turn this clockwise, it
increases the carburetor opening
at idle and increases idle speed.
Turning it counterclockwise
decreases the opening and idle
speed.
Low-Speed Needle
As you turn this clockwise (leaner),
less fuel enters the engine.
Turning it counterclockwise
(richer) allows more fuel to enter
the engine.
Richer Leaner
Idle Speed
Screw
Faster Slower
High-Speed
Needle
Carb Opening
Leaner Richer
Low-Speed
Needle