ORIGINAL: rainedave
I am using 10% Power Master to which I added enough Benol castor to bring it up to about 22.5% oil. It does have an A3, so maybe I'll try again with a #8. It has decent compression and turns freely, that is, I can't feel any binding or roughness. Is a 9x4 too much prop for an FP .20?
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A 9x4 is the perfect prop for the .20FP, as is an 8x7-8 or a 10x4.
Is it possible that the engine hasn't been broken-in previously?
There were several versions of these engines sold. There was an ABC original and an then the later ABN version. There may have even been a lapped piston/liner version, but I'm not sure. If it is the latter, it will need a considerable amount of running in a fat, rich four-stroke before it will come in and stop overheating when peaked out.
As others have indicated, if the plug is too hot, it will advance the timing way too far and this will cause overheating and refusal to peak out.
Ed Cregger