Briggs and Stratton engine

[Barney]

Sorry if this is slightly off-topic, or not quite the right group for thi, but if any of you have knowledge of these engines I would be grateful for some help. The engine is a 3.5HP one about 25 years old. It runs reasonably well until you increase the revs and then the flywheel key (the square bit that turns the engine for starting - I don't know what else to call it) seems to engage and drives the starting coil, which makes a terrible screeching sound and threatens to wreck the mechanism, we have to shut it down at this point. Anyone got any ideas what the problem might be?

[Jb]

sounds like a broken spring in the recoil mechanism allowing it to engage when the revs rise, but i may be wrong, if i am someone will jump all over me and put us both right :)

[Barney]

Sounds pretty plausible to me - and, even if it's not the problem, I appreciate you trying to help. Many thanks.