Fine tuning the low speed mixture setting (Pro .15)

Article #50457


The low-speed mixture screw is located in the end of the throttle shaft. The low speed mixture affects the idle quality and the low end engine power and throttle response. To check your low speed mixture setting, perform this simple test.
1) Drive the vehicle for several minutes until the engine is in its normal operating temperature range.
2) Pull it in, stop, and listen to the idle speed. If, after a few seconds, the idle speed begins to drop then lean the low speed mixture 1/8 of a turn (clockwise) and retest.
3) Continue leaning the engine in small steps until the idle speed will stay even for at least 20-30 seconds after stopping.
4) The vehicle should accelerate quickly from a standing start without bogging. The idle should be smooth and consistent. Lean the mixture 1/8 of a turn (clockwise) and re-test. If you experience any stalling or hesitation when accelerating, then the low speed mixture is too lean. Richen it 1/8 of a turn (counter clockwise) and retest.

Second test
Pinch the fuel line to the carburetor and observe how long it takes for the engine to stall. If the engine stalls immediately, then the low speed needle is probably set too lean. You should be able to pinch the fuel line for 1 or 2 seconds without stalling the engine. You should also hear the engine speed up just before it stalls.

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