This is the rule of thumb we have used for years

LPG CARBURETOR ADJUSTMENT

Idle Mixture

Turning the idle air screw in will make the fuel mixture richer.
Turing the idle air screw out will make the fuel mixture leaner.

The idle air fuel mixture is best adjusted only with a engine CO exhaust analyzer and the mixture should be adjusted to 0.30 to 0.70 percent carbon monoxide.

Alternate Method:
* Adjust idle to 400-500 rpm
* Turn idle air screw out until engine starts to run rough.
* Turn idle air screw in approximately ¼ turn to ½ turn or until engine smoothes out.

Idle Speed Adjustment
Turn the idle speed screw until the idle speed of the engine is within specification.

Power Adjustment
This setting is preset at the factory and should not require further adjustment. This adjustment controls the mixture when the gas metering valve is withdrawn from the jet. It is only effective when the engine is near a full-load condition. This can only be set with the engine loaded or at a close to its rated governed rpm.

If adjustment is needed, follow these steps:

* Set parking brake and block the drive wheels
* Connect a tachometer to engine.
* Accelerate engine to full governed rpm.
* Pull backward on tilt lever until pump reaches hydraulic relief bypass. The rpm should drop according to the spec for hydraulic bypass (typically a 250-500 rpm drop). If the rpm does not drop, check and adjust the hydraulic pressure before you continue.
* Turn the power mixture valve until the highest engine rpm is reached at 0.30 to 0.70 percent carbon monoxide.