Needles are pre-adjusted by factory default. By turning the needle clockwise, you lean the fuel mixture.
By turning the needle counterclockwise, you richen the fuel mixture. Needle settings will vary based
on different conditions, such as altitude, temperature, fuel carburetor variances, humidity, etc. When
needle settings are optimal, the engine will clean out and have a strong sound, high-pitched whine at
full throttle. It is always better for an engine to run a little richer than to run lean.
Step 1: Turn both high and low needles clockwise gently until they stop. Do not over tighten the needles.
Step 2: Turn both high and low needles counter-clockwise to regulated points.
The general starting points of needles are as follows.
Caution: The needles get damaged when they are tightened with too much force. Adjustments to
carburetor cannot be made once the needles are damaged and therefore must be replaced.
Symptoms of Running Lean
When a carburetor is running lean, the fuel-to-air ratio is off because the carburetor is distributing too
much air. (1) Signs that high needle is too lean include engine stalling on acceleration and beginning to
slow down at full throttle, abnormally high temperature on cylinders (overheating) (2) Signs that low
needle is too lean include difficulty in starting the engine and rough idling. In general, typical symptoms
of a lean mixture are:
Backfiring as the throttle is closed
Lurching acceleration
White or light gray spark plugs
Requiring excessive amounts of choke to run/start
White or light gray muffler end pipes
High temperature on cylinders
Understand the Engine Terms “Rich” and” Lean”: The needles on the carburetor regulate the amount of air and fuel (air-fuel mixture)
that enters the engine. When the air-fuel mixture is “rich”, there is too much fuel. When the air-fuel mixture is “lean”, there is not enough
fuel for a given amount of air.
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