I have a mature MW Powrkraft 18/42 mower with hydrostatic transmission for which I have zero documentation. The engine is a Briggs Stratton V-2 flathead which doesn't seem to want to run properly any more. It is very sensitive to 'aged' gasoline (more than a couple of weeks old). It starts fairly easily when choked, but is very tempramental from then on. It runs pretty well under load (blades engaged) but will not idle if not under load. Lopes like an antelope at more speed and dies at idle speed! Two questions. Any suggestions about why it has become so delicate? Also I cannot find any information about the engine on the mower. No numbers anywhere that I can see. Any guidance as to how to determine exactly what it is so that I can buy a service manual? Many thanks.