I have a 2003 rev with the 600 ho carburated motor in it. The machine starts perfect ,runs good etc. Both plugs are identical tan color. Never fouled a plug. Belt is new. But from idle to about 5k rpm it seems to burble, then 5k and up it takes off like a bat out of hell. after 5k rpm engine is happy. Makes going slow and taking off aggrevating. dealer said carb boots may be leaking, I looked at the boots and they look ok, but I can only see part of them without pulling the carbs. I have had this sled since new and it has always seem to run like this. any suggestions on what to do??? thanx