The plug is good. All the fuses are good. I cannot find any bad grounds, shorts, ect.. Not sure what to try next, maybe the voltage regulator????

 

i would check for dirty connections as well as like you said the voltage regulater and test the stater to.

 

Reminds me of an experience of friend and his BMW bike. Tuned it up and adjusted the carbs and it sounded great. Got on it and it ran like crap. Went through everything again, cranked it up and sounded great. Got on it and it ran like crap. Several more times through of the craziness.

While he had a spark plug out, for some reason, he turned it from electrode up to electrode down. The insulator slid down and covered the electrode! It was broken out of the box. When installed at a slight angle it was fine. As soon as the bike was tipped a little, the broken piece slid and kept the cylinder from firing.

If this does not help you, I hope it at least entertains you,

Matt B