Mikuni BS34 Has Me STUMPED!

Final update: I believe the entire problem was due to adjustment of the pilot jets. Everywhere I read it was 2 -2.5 turns out. Well, when I played with it a bit more I discovered that AT SEA LEVEL, it worked best at about 3.5 turns out for my bike. Once I adjusted the pilot jets it helped tremendously. It's still "cold blooded" and needs some tuning to really idle right, but at least I know it's NOT dirty carbs, bad valves, or ignition. It turned out to be a simple adjustment that kept me from riding for the last 2 years (tears anyone?). Anyway, I hope that my fiasco helps someone else with their bike. Cheers!

Pilot jets are not adjustable. Hopefully you are talking about the pilot screws located on the top front of the carb body.

After reading this post front to back, I was surprised that no one mentioned ultrasonic cleaning for carb cleaning. Seems like its the cat's meow anymore, for getting the carbs' passage ways cleaned out thoroughly and with confidence.

A check of the fuel levels in the float bowls, and a carb sync wouldn't be a bad idea.