Motorcycle Repair: SP500 loses compression, combustion chamber, pressure test

Question
Hello,
I've got an early '80s Suzuki SP500. I starts great, with lots of compression, then after about 30 minutes of hard riding, it dies. When I try to restart it, the engine free spins easy while kicking it. So I let it cool down for 30 minutes, then it takes off again! Any ideas what could be causing this? I tried a bigger main jet in the carb, and that didn't seem to change anything.  

Answer
Hi Steve,

Pressure test the cyllinder/crankcase to verify the integrity of the combustion chamber's sealing properties.

Perform compression and leak-down tests with engine at operating temperatures.

I'm not sure, but I suspect clearances are expanding as engine reaches operating temps.

Respectfully,
Mark Shively