Its the compression release...Our you have to much Oil in it..Check the oil, sometimes gas slipps by the rings and build to much pressure in the crank case...Otherwise you gotta have the compression release fixed..

Try rolling the engine backwards until you are all the way up on the compression stroke in reverse. Close the throttle, choke the engine, and hit the starter. You should have enough flywheel inertia for a good starter and battery to pull the engine past compression even without the compression release operating.

My ST12 would never roll over with the throttle open.

Where is the compression release located. Whats it look like? I didn't see any such part on the sears parts list
Greg
614-440-6484

I've never torn down an Onan or a Tecumseh, but on a Briggs it is located on the camshaft, which is inside the crank case.

Its on the Camshaft...its a little arm with a spring on it on the back side of the camshaft..If you pull the side cover off the engine (its on the pulley end of the engine)..Then you can remove the camshaft and inspect the compression release..But dont lose the pushers for the valves because they will fall out of the block when the cam is released...

Make sure your valve lash is not too loose before any tear down.

oh ya good call on that...Check the valve gaps..How do you tighten them up though on the HH series engineS??Theirs no adjsuters??So you have to have the seats cut or new valves installed right???