Some answers to the questions you gents have thoughtfully posed above. The back plate gasket looked good when I disassembled the engine some time ago.
Steve: I'll keep in mind the needle valve and compression parameters you stated when I fire it up again tomorrow eve. And I'll definitely use your CP reset technique. When I posted the problem, I thought that if it didn't reset during a run then nothing else would do it. Live and learn, eh?!
Chris: The bit of extra castor oil amounts to about one cc in maybe 300 ml of the Davis ABC fuel.
Chris and Ray: I like the way you guys have asked me to verify my RPM estimate - no since speculating if I'm tone deaf and my estimate is way off!
I'll see what I can do about getting a friend who has an I-phone to help me with a post to U-Tube. That's really the only way to go on something like this as you've suggested.
Ray: The NV setting of only a turn and a half does seem strange, compared to your recommendation of four turns. I'm certain that I am running it at the turn and a half out because I've checked it with the locking nut loosened. As I mentioned, it has seemed optimal in past runs, but I will double check again tomorrow. Could this leaner setting be consistent with what appears to be a smaller intake in the photo I posted above?
I've been running the engine in the garage (with open door) and enjoy the residual smell whenever we go out to the car!
Thanks.
Dave...