QuestionMy bike is a water cooled, normally aspirated 900 inline 4.
It has not had much use in the past 6 months and the fuel would be at least 6 months old and the tank is about one third full. When I started her up to give the engine a run, as she warmed up she started emitting a whitish grey smoke. When I was last riding it regularly, there was no smoke at all, she was running well after fitting quite a few new ignition and carby parts.
The bike has been in a carport under a bike cover, and the past three months has been very humid weather. Is it possible that the smoke is being caused by water evaporation inside the tank which has dripped into the fuel?
My plan is to drain the tank and fuel bowls and refill with fresh fuel and am hoping this will remove the smoke production. Am I on the right track here?
AnswerJamie, leaving a bike unused for most of 6 months with old fuel in a partially filled tank is a recipe for water production and fuel separation.
Several problems occur with today's fuels. While it is fortified with alcohol in the original blend, in a couple of weeks the alcohol will drop out of suspension, separating into a twin layer of evaporating fuel and alcohol lying at the bottom. Alcohol attracts water molecules, so any water droplets formed in a partially empty fuel tank will often be drawn into the fuel system, through the fuel filters and into the float bowls.
So, potentially you have three ingredients in the fuel system and carburetors... gasoline, alcohol and water. The carburetors were calibrated for straight fuel blends only. Often either the water or alcohol is drawn into the pilot jets and can get lodged there, plugging up the idle circuits, causing the engines to start hard and to stall at idle speeds.
So, your plan to drain the whole fuel system is valid. In the future, add fuel stabilizer to the fuel tank regularly, especially when the bike is not being ridden consistently.
Realize that when you first fire up a bike after sitting for a long time, that you will get both moisture condensing and evaporating going out the tail pipe, plus some residual fuel/oil vapors that are all heating up and burning off. Once the bike is fully warmed up, the smoke should stop completely..... if it doesn't, the remaining possibilities are a blown head gasket, worn rings or valve stem seals failing.
Bill Silver
