RE: RCVsa120
The rpm is definitely low, you should be able t o peak the motor to 5.5K, but only after run in.
If the engine has only run 5 times then it hasn't even started to free up.
Most reports are that at least a gallon or two is required before you will get it to loosen up and get that 5K to 5.5K top end.
Be aware that they also peak out at less than full throttle and then tend to bog down when opened out further.
I have seen a recipe for the run in that calls for a tank of fuel at 3K, then a tank at 3.5K, then another tank at 4K, and so on.
How is the vibration level?
Has it blown the end off the muffler yet?