QuestionI sir, I just bought for almost nothing an old honda cm 400 1981 with 39000kms. Even if the spark plugs are old an carbonized(the bike has been garaged for 2 years)it start quite well and roar like a brand new. The problem is that even if I changed the gas, a blue fume gets out of the pipes. Since the plugs don't have oil on them and compression is okay, I don't think the motor is burning oil. Where does comes the the fume or should I worry?
Thanks and sorry for the bad english, i'm not perfectly bilinguial. p.s. do you know good detersives to help with rings and cylinder carbon?
AnswerJean-Pierre... I would suggest that you do a full tuneup, including valve adjustement, camchain and balancer chain adjustment. If it sat for that long, there are problems with blocked passages in the carburetors, more than likely.
There are also small rubber diaphrams on the side of the carburetor, related to anti-backfiring control. You may have problems with the diaphragms there or internal fuel leakage/control problems with jets or passageways for the air mixtures.
Blue flames are generally unburnt gasoline vapors lighting off in the mufflers. Sometimes some oil byproducts can collect in the mufflers, as well and the bike will smoke but not use oil, in the beginning.
If the mufflers are modified, then the carburetor calibration will be incorrect for correct running.
You can try some automotive fuel additives, but in very small portions to try to clean the carbon out of the pistons.
Bill Silver
