So My brother picked up this RM for a song, it had been sitting for 6 years or so. PO parked it because it was acting up and running poorly. Bro does everything I tell him to do, disassemble, clean, lube, check wheels, clean filter, clean tank, clean carb, adjust clutch, check fluids ect. new plug fresh premix. Come to find out after washing the muck off the bike is in great shape probably less than 50 hours on it. Bike fires up and he rides it a few times for several minutes each with no issues. Gets the idle set on the carb, reports having trouble setting the idle... Fast forward the bike dies one day after running for several minutes. Won't start up again. Checks spark, gas, and compression by "feel". Checks out, it should run! Bike will not start. This happens on 2 different occasions. runs fine, gets hot, dies. has spark, gas and compression. We both decide to inspect the top end, bro takes apart and notices a small scuff on the intake side, nothing major we think. He takes piston and jug to machine shop to get checked out. everything looks good, machinist scuffed the cylinder up. he also got new rings and gapped them for him. piston is fine enough. Bro gets the bike back together today and gets it running. takes it for a few short trips around the block. runnning for maybe 20 mins or so. bike dies, won't start. Spark, Gas, Compression. nothing:huh. I'm thinking electrical issues myself, bike gets hot, coil or cdi malfunctions. Throws weak spark or bad timed spark? Remember he insists it has spark immediately after dying.. However my worry is now an air leak? or a bottom end leak? When it was running he having a hard time getting a good idle. This would certainly cause that. Maybe we have two issues going on? air leak, and electrical issues? Or maybe an air leak that gets really bad when the engine gets hot? I was very admit if he gets it running again to check for spark right away when it dies.. any thoughts?