I got a few breaks in the rain. Spun the head around again and it absolutely works better with the plug to the rear. I don't really know why but there is no doubt. I read about the cooling fins to the front, but it is 10c and raining here today. Cooling is not an issue. Plug to the front I get loping and 4-stroking, lots of rev on downhills but less torque on hills and over heating, turning the plug white. I suspect the torque on hills and overheating is a pre-ignition problem. I can hear death rattle as it heats up (I back off the throttle). Plug to the rear I get steady power, tan plug and good torque on hills.
This is only the 3rd tank of gas in this engine. The 20:1 did sound very rich, I'm used to 50:1 in my KTM but hey, follow the book, right. Next tank I'll try 32:1. This plug seems a bit hot, and maybe the exhaust side of the head runs just hot enough to put it over the limit?
This is the beauty of these engines, 5 minutes to spin the head around. Awesome! So simple to work on and experiment with. I bought a spare $30 cylinder so I can experiment without fear. I'll try to send photos of my progress.
I put the engine together totally stock, including undersized gaskets. One by one I will fix things up and see the progress. The hill and a GPS should give me a measure of progress. Even completely stock, I am very pleased. Quiet and strong, even at low rpm. Vibrations are not bad, and it goes faster than I can pedal the mountain bike.
Steve