On Wed, 11 Sep 2013 16:36:15 +0200, JBL2527 wrote:

The powered lawnmower has a Briggs and Stratton engine, normally
bullet-proof. A couple of weeks back the bolt holding the fuel tank to
the body worked loose and the tank was wobbling.

Body of the engine or the underside of the carburetor?

I had similar when one of the flap valves that are formed from the
gasket between the tank and carburetor got stuck/misplaced. Suggest
you take the whole carb/tank assembly off the engine and check that
the gasket between tank and carb is in the right place and the flap
valves are OK.


Or the governor links have been disrupted either by the loose tank or you
tightening it.

Mike