If RPM moves on its own into the yellow or red sector, check the friction adjuster for the throttle quadrant. Also check the oil pressure—following a loss of oil or oil pressure, the propeller governor sets a high RPM automatically. In this case the RPM should be regulated using the throttle. If the oil pressure is normal, pull the RPM lever back and listen for an associated drop in RPM. If the indication does not change in spite of an audible drop in RPM, the gauge is probably defective. If there is no audible drop in RPM, it is probable that  governor system is defective and RPM should be regulated using the throttle.

If loss of RPM occurs, check the throttle quadrant to make sure the friction adjuster is sufficiently tight. If this is not the problem, try turning on the fuel pump and switching fuel tanks with the selector. Finally, move the RPM lever to HIGH. If there is no audible rise in RPM, it is probable that the governor system is defective. Control RPM with the throttle. If there is an audible rise in RPM after moving the lever but no corresponding increase shown on the gauge, the gauge is probably defective. If the RPM cable breaks, control engine power with the throttle. If the throttle cable breaks, control engine power with the RPM lever.