Carburetor Setup & Adjustment:

Be advised that I have modified these instructions for my own use. Use them at your own risk.

Carburetor Setup & Adjustment

All settings should be done with the choke disengaged or warmed up so that the choke is fully opened and disengaged.

Baseline settings:

Set the idle stop screw/speed screw:

  1. Back it out until it is not in contact with the throttle stop lever.

  2. Cycle the linkage to be sure that the linkage closes without any assistance.

  3. Now bring the screw back into contact with the lever and continue to open or screw in 1 to 1½ turns.
Set the mixture screw:
  1. Screw it in until the screw stops and bottoms out. DO NOT FORCE OR BIND IT as this will cause damage to the screw and its seat in the body of the carburetor.

  2. Then back out the screw in two full turns.


Start the engine. The engine will run very slowly, much like a tractor. As long as the engine stays running, idle speed is not important at this point.

Adjust the mixture screw:

  1. Turn in the mixture screw until the engine dies or runs worse.

  2. Back out the screw ¼ to ½ turn at a time. The engine should pick up speed and begin to smooth out.

  3. Back out ½ turn more, or until the screw does nothing or runs worse.

  4. Then turn it back to the point where it ran its best. Adjust to best, fastest and smoothest running point.
Adjust the idle stop/speed screw:
  1. Turn the idle screw in ¼ to ½ turn at a time until an idle of around 700 – 900 RPMs is reached.

  2. Also test while transmission is in gear and clutch let out enough to provide a slight load

  3. Adjust it to the best running condition.


If the mixture screw is more than 2½ turns out, then the idle jet is too lean/small. If the mixture screw is less than 1½ turns out, then the idle jet is too rich/large.

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