Get a cht to see what your temps are.
I'm running a 19mm phbg but it's a points bike. I have no curve in my timing.
It runs pretty cool now after I did my fan cooled mod.
Still gets to 400 but I have to climb some ridiculous hills to get there.
Keep in mind, it's the tuning once everything is sealed right. There are plenty of folks on MA that run no cdi or Wc kit and can ride for hours without problems. If it is shutting down every 20min, you've got other issues...