mountfield sp470 engine hunts

[advinnie]

Hi all ive just got a second hand mountfield sp470 lawn mower it starts first time every time but just after roughly 5 ish seconds the engine starts to hunt. I have found a leaver at the front of the engine next to the air filter that seems to control the rpm. When moved one way the rpm increases but then the engine starts to hunt but if I move it the after way the rpm will drop but the huntting will stop. It does look like there is something missing like a spring. Is this a choke and is it normal for the engine to hunt when I increase the rpm? Cheers

 

[Mursal]

Usually on Briggs and Stratton engines the choke is at the max position on the speed control up on the handle? To knock the choke off, you just move the control a tad? If not it will be a small lever next the air cleaner box?

The lever you are talking about is the governor control and will cause this "hunting" of the engine revs. As long as the air filter is clean and its cutting as it should I wouldn't over stress about it. It probably doesn't hunt when cutting?

Stuff
http://www.jungle-busters.co.uk/Lawn-Mower-Spares/Mountfield-HP470-SP470-Spares

 

[Burnerman]

Many of the B&S engines have no choke, just a primer bulb on the side.....the throttle control is either for fast or slightly less so, and then the governor takes over.
I imagine your machine is just a push one?
The engines, as Mursal says, do tend to hunt until they come under load.
John

 

[advinnie]

Hi there the air filter is clean and and the engine only has one speed there is no control on the handle it is ever on or let go of the handle and it turns off. If I move the level by the air filter so the rpm is high the engine will hunt even when its cutting but if I move the level so the revs drop the huntting stops but if I hit a thick bit of grass the engine will try and stall. Its a self propelled mower NOT a push mower. Please tell me whats this governor thing you mentioned

 

[Mursal]

Did I mention to make sure the air filter is clean

This might help
http://www.youtube.com/watch?v=LzpSy5CJL6k

Your carburetor may be slightly different

 

[Burnerman]

The hadle you mention is actually a flywheel brake, which has an electric cut off switch included....releasing the handle stops everything for safety.
The purpose of the governor is to keep the engine revs constant even when the machine is under load - where it would naturally try to slow down.
I think a carburettor clean is required....tell me - is the gas tank below the carburettor, or on the top of the engine?
John