Some say it may be the ignitor pickup gap. Mine does the same thing. If the temp runs up about 3/4 it starts misfiring. It died on me the other day. I two legged it over to the side of the road. crank, crank, nothing. I am saying to myself. I am sick of this piece of **** Vulcan thing. Ready to drop it on its side and call Uber. Crank, fires right up. WTF, So I red lined through four gears until everything was blurry. Regained my composure, got home and shut if off. Fan was running, then stopped. Hmmm? I have a New glass mat battery. Maybe just maybe the fan draws too much current as these bastid things are very dependent upon having minimum 10 volts to run! Definitely do the ignitor gap mod as these folks in here have been through it all with these bastid Vulcan as well. Strength in numbers, time is knowledge. I have had this bike for more than 10 yrs, second owner, put more miles on it than the first. Divorce is stopping me from a new bike, but these are quick little machines and fun to ride if you can put the little quirks to the side and just ride!