RE: OS .35 FP reving up after a while.
What you have is the dreaded "FP Runaways". These engines are not timed for stunt. The best thing I can recommend to do is to pack it up and send it to Lew Woolard or Len Newman. Lew does great work and has a fast turn over time. Len does good work as well, but takes a bit longer. It should cost about $40 or so to have that FP 35 running like a pro.
Jay