Skylane,

My first suggestion is to try a fresh plug. Try an OS #8 plug as a reference point and try others if this doesn't work.

The 12x8 is a bit too much prop for the .60 - a good place to start with this engine is an 11x7 or a 12x6.

Your fuel, if fresh, should be fine. My FSR 60 runs quite happily on 80/20 with no nitro.

Good luck - that .60 is a real keeper.