What is the safe max rpms' that you can ride without causing damage to the motor. The book says 7hp@ 8000 rpm's. Is this high? Can it saftly run at 8000-9000 rpm's for long periods of time? My son likes the snow. It only moves (in the snow) if it is in 1st gear at higher rpm's. To me this thing sounds like it is screaming but how do you tell? Also when I start it up when it is cold out it knocks 2 or 3 times really bad but then it is gone. Sounds like really bad predetonation or a rod knock. It sounds perfect otherwise. Is this normal? I am just really parinoid about blowing the motor. It does not have a rev limiter.