My 52 with the 216 did quite similar to your condition, I found the thermo flap in the manifold stuck in the closed position. Freed it up and the problem went away. That was 20 years ago and problem never has returned.
When I got it on the road about a year ago, the thermo flap was stuck open, and in Australias climate effectively boiling my fuel. Now its clamped closed and I immediately got another 10mph.
It made no difference to the pinging though. Same before and after.
Dragsix - I haven't determined that its working properly, but it is working. With the Vacuum advance, I repaired and installed the original.
Otto - thats interesting and handy to know, but I doubt it would make much difference in this case.
Jerry - I have heard of that method before. But I'm not too sure. I'd be scared of cracking the head. If carbon buildup is causing this I think I'll take the head off and clean it properly.
