I am having the exact same problems with mine. It was stock with the exception of the VF3's a airbox with K&N setup and +4 timing, I added all of the other stuff at the same time. I was running a Noss head with 21cc domes at the time and 300 mains, 27.5 pilot and clip on 4th position. Blew up after about 45 minutes of ride time total, the right piston that is.
Rebuilt it again, thinking it was too lean, went to 320 main, 27.5 pilot and 4th on needle, ran it at silver lake for about 3 hours, right side leans out again.
So now getting it narrowed to detonation this rebuild will consist of all of the same upgrades but am switching to 19cc domes and running race gas. Hopefully it works this time.