A buddy of mine just purchaced a 93 650L that has 30,000 miles on it. It ran great but smoked like a train when first started. After a few rides he started complaining of a tick in the valves so we adjusted the valves. The tick seemed to stop, but now there is a loud sharp backfire on decel. I rechecked the exaust clearances tonight and they were a little tight so i backed them off a little but still backfires. also when it backfires i notice a puff of smoke out the tail pipe. could the intake clearances be off????? any help would be appreciated thanks!!!!!!!!!!!!