Long shot, but does anyone know about the adjustment of governors on small 2-stroke generators (Yamaha, 500 watt), and governor faults?

Mine was tending to hunt (rev up and down) and I took it to repairers who just screwed the governor up until the engine ran flat out - result, far too many volts. The governor is operated by a lever coming out of what I think is the crankcase but it could be an extension of it. The lever is pulled in one direction by a spring anchored to an adjustable plate, and the position of that plate is controlled by the governor adjustment screw. The end of the lever has a push-rod that pushes the throttle butterfly open (via a cranked arm). The direction the spring pulls the arm opens the throttle.

Something inside the crankcase (or the extension of the crankcase) pulls the lever in the other direction to close the throttle butterfly.

Well, I've solved the over-revving and excessive voltage output by screwing the governor adjustment screw out so reducing the tension on the spring. But now the hunting is back.

I understand in theory how "flywheel" governors work - more revs, more centrifugal force, arms rise and reduce throttle - but I don't know whether this is a flywheel governor. There is I think another sort of governor used on 2-stroke engines - that is operated by crankcase depression. Walbro carburetters use crankcase depression and its variation to operate a little fuel pump on chainsaw hedgetrimmer and strimmer engines that need to work at any angle.


Does anyone know how crankcase depression governors work?

Or has anyone any other ideas about the hunting? The carburetter has NO mixture screws to adjust as far as I can see, and that is a first as far as I know. Every other 2-stroke I've ever taken to bits has had 2 mixture screws (one for idling mixture, and one for full-throttle mixture) and a throttle stop screw to regulate the idling speed. I have got a stop screw to limit how much the governor can close the throttle, and it's already all the way in so stopping the governor closing the throttle too much