Hey Redeye....
As someone who likes to fiddle things to squeeze a bit more out than the factory intended
I can understand where you and your mate are coming from...
"you could try finding an old power plus head and muffler and swapping those over." AS Ty suggests is the easist thing to do and will give the mower a lift.
Depending on how much trouble you & your mate want to go to I would go a new piston and rings or a re-bore and new piston and rings (see on line store on here for the parts etc)but before you do that spend some time with some wet and dry carborandmn, wrapped around a wooden dowel(sand paper)and polish out the casting marks in the ports, in the barrel, being carefull not to change their hieghts relative to the piston in the bore (make even and match up the transfer ports). Use the old piston as a gauge, maybe even up the exhaust a bit...it's up to you, it all helps...It will have more power.
Make sure all other bits i.e. Decomp valve, carby, ign., air cleaner, fuel system are good and clean. Actually it might pay to change the crankcase seals and check the main bearings while your at it!(see on line store on here for the parts etc)
Whatever you guys do; have fun!
