ORIGINAL: David Bathe
And use the 4 stroke F plug.
I dis-agree. He should run a O.S. A5 like I have it in mine. It works perfect in my O.S. 61FX. The F Plug is a long plug, and the A5 is a short plug designed for this engine. He will risk piston slapping on the plug resulting in piston damage over time if he uses a long plug.
I'm glad I helped you. Not many people know that little trick, so you will have plenty of times to teach others. When Tom showed me that trick at my Club I was flabbergasted!
Have fun and have a great flying year.
Pete