I use the same fuel as I use for my two strokes and have never had a problem. (Powermster 10%, 20% oil.)
Don't know about ASP's, but I find four strokes easier to run, and certainly prefer the torque and the sound.
I agree too with the OS "F" plug. Best on the market for four strokes. Second best has to be the Fox "Miracle" plug.
Good luck,
Dennis-