Okay, here's the rundown: 1978 Yamaha XT500, normally runs like a champ. Lately, at midrange RPM and mid to heavy accel, it bogs down, stutters, and misfires pretty bad. It has been doing this off and on for about three months worth of riding, but the problem got really bad today. The carb was rebuilt about two years ago, and I have done some minor carb repair in the past year, and it has run fine since then. I have never adjusted the points, because frankly I don't know how to do it. My thinking is it's either points or carb, but I was hoping someone here could help get me pointed in the right direction. Any thoughts? BTW, I'm a mechanic, but I work on new cars and trucks only and don't have a clue what's what on this bike. Translation: I'm good with my hands and confident with repairs, so I should be able to handle whatever you all throw at me!