There is a good chance there has been water in the fuel tank and some of it is now in the carburetor, blocking the main jet among other sins. There may also be sediment, and/or a blocked filter, and crud may have been sucked through the main jet into the emulsifier blocking up some of the tiny holes. Or the choke may just not be closing, or the float stuck in the up position due to gum formation. You already know the fuel went putrid, so the chances are somebody put fuel containing ethanol in it. Just pray it isn't a chonda, or there may not be much left of the fuel system due to decomposition of the hose and plastic parts. It is best to go through the process methodically, since you can't know what neglect or abuse has occurred.
Last weekend I bought a Ryobi pressure washer powered by a chonda copy of a Honda GXV160. It apparently had run less than 20 minutes since new (the tenant had tried to use it for hydraulic mining on a building site, sucking up the run-off for intake water, and scrapped the whole machine as soon as the intake filter got blocked with clay), but it also had just a few drops of water partly obstructing the fuel filter and main jet, making it reluctant to start. The detergent suction system had been dismantled and the ball from the non-return valve thrown away - I've ordered a replacement stainless steel ball. The fuel system had to be blown out and some carburetor parts probed with cleaners. The inlet tappet clearance was half what it should have been. Otherwise it was just a new chonda, pretty much identical to a new Honda: on this one, everything else happened to be OK. However that was because in his 20 minutes the previous tenant didn't get around to ruining much else. Your mower has been in someone else's hands for years. It's best to check it over, fix what is wrong, and make it run like a Honda, whether or not it turns out to be a real Honda.
Last edited by grumpy; 17/08/12 12:08 PM. Reason: Add detail
