This has been bugging me somewhat. My bike that I have noticed has been smoking a blueish-white smoke on start-up. It is sometimes really bad, but just at start-up. After about 1min of warming up, it goes away and burns clean. The engine turns over easy and starts right away usually on the 2-3 crank with choke (10sec). I'm thinking either the carb is leaking fuel into the engine or a ring or seal could be leaking a small amount of oil into the combustion chamber. I've already added4ozof acetone into a full tank of Octane 91. Made the engine even more snappy. But it does not seem to help much.

Any clues that anybody can come up with? Anybodys else's KLX250 does this too?

 

How many miles on it and have you done any mods to it? Four oz. of acetone in a 1.9 gallon gas tank is a lot - Maybe 10 or 20 gallons of gas to 4 oz. acetone!

 

The KLX250 is pretty much stock except for a new NGK CR8EIX plug and new Kenda Tires, plus Royal Purple Max Cycle 10w-40, all done at 2,000miles. The bike has 3,000miles.

 

Bluish white smoke means it's burning oil. It only smokes at start up, correct? How is your oil level?

 

Blue smoke on startup is a leaking valve seal usually.

 

Mine was smoking on startup as well but I couldn't really get a good fix on the color of it. I dropped back to the stock pilot and now no smoking.

 

My smokes on start-up once in a while but it isn't blue but black, I'm sure it's caused by the #40 pilot at this altitude.

 

What does the acetone do,why put it in the gas.

 

From thinking further on the problem. I'm guessing 90% that I do have a leaking valve seal. The smoke is only at the worst upon starting and clears after 1min of warming up. If I let the bike sit longer (1week or more), the smoke is more evident but still clear ups after 1min of warming up. It could be the choice of oil that I'm using. I know Royal Purple has a natural tendency to lube into further clearances. It might be passing the valve seal when cold, but when the seal heats back up, it stops. As for oil level, still at the full mark after 1,000miles.

The acetone works just like a carb/fuel injector cleaner additive that you might use when you fill-up yourcar. I just didn't want to spend $6 for B-12 cleaner and only use 2-4oz of a 16oz bottle. So I used straight up acetone cleaner. What it does mainly is to de-gum the carb and clean the valves of carbon. Some other benefits is that it increases octane levels.

The KLX orignally came from Gaum. A US airforce man brought it to the states and sold it to another airforce man which he sold it to me. So I'm the third owner at 1,800 miles. So I think the KLX is set for sea level fuel mixture, but I'm only around 1,000ft higher, the fuel mixture should be good since it doesn't puff black smoke.

 

+1 on the valve stem seals. Those are classic symtoms. Not much to worry about really.