Motorcycle Repair: 1981 Yamaha 750 virago, valve stem seals, piston ring

Question
Hi Bill, since it is an older bike thought you might be able to help.  My 1981 750 Virago is in very nice shape, but i have a problem i can't figure out, it runs great for days then starts running on the left cylinder only, i change the sparkplug on the right side and it will run great a few more days then the same thing.  The plug doesn't get sooty but slightly damp. Carbs have been cleaned /new air filter? i am baffled.  Thanks for any assistance you may be able to give me.  Ken

Answer
Ken, it sounds like it is oil fouling, rather than fuel fouling the spark plug. Depending on the mileage it could have piston ring wear issues or more likely is needing new valve stem seals.

Check compression and watch your oil consumption for more clues about the cause of the plug fouling. Look for some blue smoke out the exhaust especially after prolonged idling, descents down long hills and often first thing starting up after sitting overnight or longer.

Bill Silver