Base Start-up Settings from the Factory
High-Speed Needle -- 4 turns out from bottom
Low-Speed Needle -- 2.5 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.
The low speed adjustment affects both the idle and slightly above idle
performance. The optimum setting allows the engine to idle for at least 8-10
seconds. The truck 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 this long,
turn the idle screw clockwise, increasing the idle speed. While the engine is at
idle pinch and hold the fuel line near the carburetor, cutting off the flow of fuel and
listen to the engine RPM (speed). If the low speed needle is set correctly the
engine speed will increase only slightly and then shutoff. If the engine increases
several hundred RPM before stopping; the low speed needle is rich. Lean the
mixture by turning the needle clockwise one hour. Perform the same test again
by pinching the fuel line. If the engine speed does not increase but shuts off the
needle is too lean and needs to be richened by turning the low-speed needle
counter-clockwise one hour. Perform the same test again by pinching the fuel
line. After you have optimized the low-speed needle setting; the engine may be
idling faster. You will have to adjust the idle stop screw counter-clockwise to slow
down the engine idle speed. The engine should accelerate at a constant pace
without hesitating.
1
Ho
ur
2 H
ou
r
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.
Low Speed Adjustment
Idle Speed Screw
As you turn this clockwise it
increases the carburetor
opening at idle and increase
idle speed. Turning it counter-
clockwise decreases the
opening and idle speed.
High-Speed Needle
As you turn this clockwise
(leaner) less fuel enters the
engine. Turning it counter-
clockwise (richer) allows more
fuel to enter the engine.
Low-Speed Needle
As you turn this clockwise
(leaner) less fuel enters the
engine. Turning it counter-
clockwise (richer) allows more
fuel to enter the engine.
Richer
Leaner
Hi-Speed
Needle
Carb Opening
Leaner
Richer
Low-Speed
Needle
Idle Speed
Screw
Faster
Slower
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