I melted a piston in my 95 Wildcat EFI this weekend. I had just ridden about 20 miles of tight trails with no problems, it seemed a little low on power but it was 0 degrees celcius out so I didn't think much of it. I got on the lake and was cruising at around 85mph for maybe a 1/4 mile when the engine stalled. When I came to a stop I restarted it but it ran very poorly, and I could feel in the rope 1 cylinder was lacking compression. I pulled the plugs and the PTO was a nice dark brown colour, but of course the mag side had everyones favorite aluminum grey colour...damn. I limped it home and pulled the head, to find a hole melted through the center of the piston. I am wondering what would cause this. I had a full tank of 87 Octane, I usually run higher but I'm 19 and I don't have too much spare cash so I cheaped out. I noticed the exhaust was leaking at the MAG pipe, theres oil all around the bottom of the cylinder. The only other thing is that I replaced the base gasket on this cylinder 350 miles ago, It blew outwards from the coolant passage, no internal leaks but the temp light did come on (I shut it off immediately.) I haven't torn it down yet to see if there are any obvious causes, I am thinking either the crank seals or the gas, but I see a lot of people on here have had Wildcats so any insight would be greatly appreciated. Thanks,

Joe

sounds like you lost a gasket and it sucked air :(

If you have a hole melted through then it was caused by a lean running condition, here are some possibilities

Air leak in crankcase or cylinder base
Too much air, air box cracked? cracked intake manifolds? Oil injection line broken?
Shortage of fuel, injectors? sensors? Frozen? Fuel Pump?

It's strange the temp light came on, the temp light only works off of coolant temperature and of all the motors I leaned out it never came on. I did have to change a thermostat on a wildcat once.

My exhausts have always leaked a little between the cylinder and the manifold, not to worry there!