i have 2 650 assaults ,,, sled 1 started on day 1 with engine surge at 5000 rpm ,,, and at no other rpm or speed ,,when you try to hold a slow speed at 15 to 20mph or at 5000 the engine will go from 15 to 24 mph or 4800 t0 5400 rpm with out moving throttle ,, hard to drive on rough or slow tight...