yamaha champ 100

[lon]

I have a 87 yamaha champ 100 that smokes. I had it rebuilt a while back and it ran great. About a month after it was rebuilt I let a friend borrow it and when he brought it back, it was popping, smoking and wouldn't hardly run. Well it sat in my garage for about a year and a half until I got around to taking it to a shop. Come to find out someone put a different plug in it that was too long and a valve hit it. I got it back from the shop, it runs good now but it smokes alot. What could cause it to do this.

Thank,
Lonnie

[Logan #34's Dad]

rings, jetted two low or high depending how you interpret (If it has a 130 main put in a 128 etc.) Since you stated that it bent a valve it must be a 4 stroke so the oil mixture would not be it. Those are the two obvious things I can think of.

[lon]

I don't think its the jets. I had the top end rebiult about a month before by buddy borrowed it. Could bending a valve mess up the rings? Do 4-strokes have crank case seals?

[Whitfield]

Black smoke is fuel.

Blue smoke blue is oil.

Maybe try a compression test.