Setting the Needle Valves
When tuning the needle valves for maximum
performance, adjust them in small increments,
1⁄16 turn at a time.
An engine should not be run too lean; doing so
severely shortens the life of the engine. When an
engine is set too lean, it will run very strong at
first but will soon begin to sag and hesitate or stall
when accelerating.
The best way to tune an engine is by using an
infrared temperature gauge, but you can also use
water to check the head temperature (refer to “Tuning
the High-Speed Needle”).
Tuning the High-Speed Needle
To obtain the correct high-speed needle setting, start
the engine and drive your vehicle around for a minute
or two, applying full throttle frequently. Place a drop
of water on the cylinder head. If the water sizzles away
(evaporates immediately), the needle setting is too
lean. A correct needle setting will result in the water
evaporating after 3-5 seconds. If the water does not
evaporate, chances are good that the needle setting is
too rich. Lean the needle 1/16 of a turn and run the
engine again, adjusting the needle setting to get the
desired evaporation time.
Check the temperature each time you change
the needle mixture. Do not let the engine
overheat, as this will damage the engine.
Tuning the Low-Speed Needle
The low-speed needle (also referred to as the idle
mixture or idle needle) should be set after you’re
satisfied with the high-speed needle setting. After
achieving the proper operating temperature, reduce the
engine throttle to idle and pinch the fuel line with your
fingers close to the carb fuel inlet nipple. If the engine
dies immediately, the low-speed needle is set too lean.
If the rpm’s increase dramatically, the setting is too rich.
The ideal setting results in the rpm’s increasing just a
slight amount after pinching the fuel line.
Engine Maintenance
Periodic maintenance must be performed in order
to keep your engine in proper operating condition.
After each day of running, it’s critical to use high quality
after-run oil to protect the internals of the engine and
help prevent corrosion. The methanol used in the fuel
attracts moisture that can cause corrosion (particularly
in the ball bearings). Follow these steps after running
your engine:
1) Empty all fuel from the tank and fuel lines.
2) Remove the glow plug and air filter and add
5 to 6 drops of a quality after-run oil into the
carburetor and cylinder head openings. Turn
the engine over a few times to distribute the oil
throughout the engine.
3) Clean and inspect the engine, air cleaner and
fuel system.
Troubleshooting Guide
Problem
Engine won’t start
Engine starts, then dies
Engine starts and runs
for 1⁄2 tank, then quits
Idle Stop Adjustment
The last setting to be made is the idle stop screw.
Turning this screw clockwise increases the idle speed,
whereas turning the screw counterclockwise will
make the engine idle at a lower speed. Ideally, the
engine should idle just fast enough to be reliable in
acceleration and transition from idle to full speed.
Avoid an idle speed that is too fast, as it will cause
damage to your clutch.
Possible Cause/Solution
• Clogged fuel line
• Bad or improper glow
plug
• Glow igniter not
charged
• Engine flooded
• Pressure line blocked or
disconnected
• Bad glow plug
• High-speed needle too
lean
• Hole or tear in fuel line
• Bad glow plug or idle
speed set too low
• Overheated engine
(too lean)
• Improper needle
settings
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