Had the bike out Saturday for the first time in a long while. One of my 640 mile round trips to Norfolk and back. Bike seems to run fine, loads of power and fuel economy as expected. But I have a lot of popping and backfiring on the overrun and quite an uneven idle. Over winter I checked the valves (none adjusted), oil and filter change and replaced coolant. Nothing there that would cause this in my mind. The only thing I have done is take the db killers out of the cans. Have been meaning to balance the carbs, but not gotten around to it yet. Any thoughts?