RE: Magnum 120FS RPM issue
With a MA 15/8 K Prop, I'm turning 8500 rpm after 2 gallons of 10% nitro, 20% oil. I would pull cam cover and make sure the com its indexed correctly and check your valve clearances. It will only turn about 8000 before its broken in. With the piston at tdc the cam dot should be in line with the push rod tubes. engine may not be properly tuned, either to rich or lean.