My 1990 CBr250rr is blowing a blue colored smoke when i start it but it only stays for about 2 minutes then goes away and i have had someone follow me and there is no smoke when i ride even when i give it a lot nothing at all only seems to be when i start it and its not even every morning just most and i really don't know why.

 

Probably condensation in the exhaust

 

Blueish smoke is usually burning oil... does it smell at all?

 

it does smell a little bit i got told from a friend that it might be a valve seal but i really dont nkow what that is i very new to bikes and just worried about my bike.

 

Sounds like valve stem seals or even just one is allowing oil to seep down into a cylinder. It takes F all oil to create a decent amount of smoke. The fact that it is worse on start up and then goes away suggests to me a worn valve stem seal. Even if it's only one I'd change them all while going to the trouble of either doing it yourself or getting it done.

 

If it only does it on start up when cold, I wouldn't worry about it too much. The vavles could be an issue, but it really isnt going to hurt anything if they leak a little. All that is happening is the oil that has pooled up around the seal is leaking down into the cylinder when the engine is no running. When you start the bike, it burns off the oil in the cylinder. If its the valves that is causing the issue that is.

Another thing to consider, if its only slightly tinted blue is it may be just be running rich. Since your probably using the choke, it is going to richen the condition slightly. Normally, rich conditions will present black smoke, but if its only a slight amount, it can also be bluish as well. I only suggest this since it is happening for a few minutes. Worn vavles will usually only do it on initial start up as the oil is burned off really fast.

Of course, it all depends on how bad it is smoking. Is it smoking just sitting at idle? or are you revving the engine? Maybe post a video?

you mentioned it smells a little. Does it smell like gas? or like oil?

Another thing to look at is your air box. Make sure you aren't getting any blow back into the air box from the crank case. That may explain the longer time period you are seeing blue smoke at start up.

Make sure your not overfilled on your oil as well.

 

Couldn't agree more.

 

agree, gasoline from combustion chamber and burning oil makes blue smoke due to bad piston ring.