RE: OS .25FP Any good???
The blue head and the rest of the motor for that matter is an OS25LA the successor to the 25FP.
Just one word on fuel. While the 25 will run on R/C fuel it needs a higher oil content then many of the cheaper brands of fuel. It is a plain bushing engine and needs more lubrication then a ball bearing equivalent. Something around 20%oil is at least the minimum that I would use. I personally run Powermaster 10/22 in most of mine but Sig and some others are all good. Stay away from all synthetic fuel mixtures for C/L. Since you have no throttle control if you go lean in flight you will have to run the tank out in that condition. Lifespan of your engine can go down the drain immediately. Bottom line is use a fuel with some castor in it.
dennis