May 29, 2000
Maybe someone out there can help me with my problem.

I just put a .60 over Wiseco 10:25/1 piston in a 88 XR200 motor that had Powroll's stroked crank in it. I was running a 120 main jet and 92 octane, the balance of the engine is stock with the exception of a ATC big fin cylinder.

When first running the motor I could hear a little rattling off the bottom which I thought it was the timing chain. It also had a real kick at TDC when starting.
I broke it in properly and in my first harescramble with it, started overheating and finally blew part of the crown off the piston just off the to the side of the intake.
When examining the piston it looks like a lean condition with the burnt /melted aluminium dusting on the top and the heat score marks on the side.

Is a 120 Main too lean, it seemed to run fine with this.
Do I need higher octane fuel.
Is .60 over to much for these cylinders, I'm using a big fin ATC cylinder so I thought the .60 over piston listed for ATC would be ok.

Someone must know about this.

I appreciate your time.



Apr 17, 2001
Sounds expensive!!!!!:eek: Most likely too lean. On a Kehin (spelling?) carb, assuming its a stock one a 130 is small main. On a 80 I used a 135. I would have used something about a 150 maybe 160 for starting point and done plug checks. Kehin jets are metric sizes from memory so a 130 is a 1.3 mm hole, 150 a 1.5 mm hole. I also feel that 92 is probably too poor quality for such high compression. Others may have more advice.


Mar 11, 2000
Kelly, you should be talking to powroll, or BBR. There is alot of variables here considering these mods. Everything from jetting, piston skirt clearance, improper fuel, crank dimensions, etc.
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