ORIGINAL: mike109
Most FP engines had ABx cylinder/piston sets but some early ones had iron/steel. The ABx type should be run at a rich two stroke for running in usually for just a few tanks, the iron/steel pistons need a long running in of very rich short runs with the mixture gradually leaned out over about an hour or so.
The "iron/steel" need 18-25% castor oil in fuel or you will shorten the engine life in your OS Max 25 FP with syntetic oil in fuel.