Mountfield SV 150 governor flap?

[Matt Clueless]

I habe a Mountfield SV150 mower on which I have recently cleaned up the Carb and spark plugs. The engine runs well but it revs high and low continually. I notice that the arm on the side of the mower swings back and forth as it revs. pic 1. I have seen similar mowers on the Web and they all have a governor flap which appears to be missing on my mower. Is it a missing part or does something else do the same job? All help gratefully received.

 

[Burnerman]

From pic 1 (some others have just vanished) it would seem that your engine has a mechanical governor, not a wind vane one which is only prevalent on small Briggs motors.
The reason it is moving is this.......the engine speeds up, and the governor regulates it a bit - when the engine slows down, the governor opens the throttle again so the engine is constantly changing speed.
This usually indicates a slight carburettor blockage still when the engine is on full throttle, so.....
Does the engine run slowly comfortably or does it tend to stall?
Next, if you can, with the engine on full throttle try to apply a tiny bit of choke and see if it stabilises a bit.
John

 

[Nige F]

Good advice as usual, Burnerman. I've got a blocked jet on my B+S Hayter but I just leave the choke half on. I've come to the conclusion that as long as the blades go round and cut the grass it can do what it likes.Easy starting is the only thing I need and it does that, not like the other one I gave my son -We've got some fuel stabiliser in it now as you suggested. I'll keep the forum posted. I wonder if the OP has a Chinese engine. My other son has a Chinese engine mower and it does that revving and you can see the governor arm @ the side moving all the time.

 

[Burnerman]

Cheers Nige
I would guess that the engine is a Chinese copy.....they work well enough but spares are a real issue so its best to look after them as far as possible, and then junk them.
Carburettor cleaning is really only successful when compressed air is at hand, but even then you have to be careful......one type of Briggs carb has a tiny needle valve seal which often gets blown out without people noticing
John