Thanks guys. I tried richening the low speed needle 1/4 as suggested and I think it helped. The hesitation from idle to full throttle is no worse that way, maybe better, and I was able to screw in the high speed needle quite a lot with no ill effects.

It's still odd, because the engine scarcely seems to respond to the high speed needle at all--it was open five turns and I screwed it in at least two turns but the engine ran the same. But it seems to run fine now no matter where I put the high speed needle.

I know about the reputation of the carb and need for low nitro, but the engine did run wide open, and with the two head shims I don't think the 10% nitro is a problem.

Between the new fuel line, the pipe thread compound on the carb parts, and a different glow plug (K&B 1L) I have no idea what actually made the difference. But it wasn't a science experiment; I just wanted the engine to run, and now it does, quite well.

Thanks again,
Jim