It is the rev limiter, it is set to kick in at about 40mph ish but I am willing to bet your belt is pretty worn which will cost a few mph off the top. Dynatec has a great cdi box that removes the limiter and would add about 8mph. If you install the cdi box you would be wise to also install a machined sheave to lower the rpm up top- The 660 doesnt like high revs for long
Hapa- ''When I checked into my motel, I said to the lady at the desk:
"I hope the porn channel in my room is disabled."
"No," she said, "it's just regular porn, you sick bastard."