can anyone help me figure out why my yamaha wolverene 350 is blowing black smoke. It idles great but when I throtle it up,in mid range it runs rough and blowes black smoke. I cleaned the carb. changed the air filter. It also spits fuel back into the air box. It seems like its getting more gas than it can burn. I've adjusted the slide piston and it helped some. could my timing be off. Any help would be apreciated, Thanks

 

Well I'm no engine builder but I've always been told black smoke means you're burnin oil probably needs new rings and a rebuild. White smoke means you're burnin water probably need a new head gasket and a rebuild. If your rings are bad it's not compressing properlly and their by not burning all the fuel off.

 

Blue is oil.
Black is fuel, too rich

That's a tough one without being there. Your needle and seat may not be shutting off, causing the fuel level to be too high. Try shutting off the fuel petcock and letting it run for a few moments, then rev it up and see if the condition gets better.

Could be plug also. Check gap and condition.

 

Too rich, try adjusting your needle clip up one notch so the needle sits further down(less fuel)