So it dropped the porcelain for the piston in the motor, or just melted the strap? I'd agree with what the others have said about it going lean. There's a million variations of why so you will have to diagnose that. Is this strictly a drag bike? If yes, and you can't get the cyld to clean up and stay in spec I'd have just that one cyld bored, new piston, put it together and run it. Yes the bores are missmatched. I'm sure I'll get flamed for this but most on here are to fucking stupid to pour piss out of a boot so I couldn't care less. You can either spend a little time with a cutting tool and remove some material from the bottom side of the new larger piston to get the weights close, or you do what I would do and just put the fucker in and run it.