Need help troubleshooting King Cat trouble, drops a cylinder over 5500rpm

Put it on a track stand, run it up to 6500 and make sure your valves are opening? Just a guess.

Power valves .......very common for cable to be off the servo motor sprocket but even more common cable brokern, visual check 1st, pull little plastic cover!!

But.......if it tends to heal its self up overnight or after warming up ( and cables don't reknit over night or reattach ) you likely have the old water / ice. snow / in thottle flipper, frozen wet connection, when a couple of my pals had these models, several times middle of day, all of a sudden crappy missing no rpm irritating no go, stop dissassemble throttle swith connections, cleaned and dried and away they go...........til next time.

The first thing I would try I would try is unplug your BD box and see if it still does it. I have heard of alot of problems with them.