My buddys bike was sputtering and hesitating a little and we thaught it was a simple jetting issue. Took it to our local race mech. and he said that the valves have blow by and the motor or the valves at least, need to be rebuilt. Is there any tests I can do to confirm this is the problem. Thanks. He said he did a leak down test to determine that there was a leak probley in the intake valve. Blowing back into the carb. Help guys... Thanks..