Still overheating

sure the timing is correct? shouldn't have to put it in drive to shut it off. could it be running lean? 6 years on the rad? was it a new rad? you sure its clean and none of the tubes are clogged?

I'm pretty sure the timing is correct. I have a timing gun and double-checked it after tightening the distributor down.

It could be running lean, I suppose, but it doesn't feel like it when I step on the gas hard. I haven't adjusted the mixture at all. I'll start from scratch with the carb then. As a baseline, do you know how many turns out should I start with the mixture screw before dialing it in?

I guess can't vouch for the radiator not being clogged, but it doesn't look very crusty inside. Is there a way to test it myself? It was new at the time. I think I picked it up from Kragen, though. :-?

I was thinking yesterday that maybe the radiator cap is not holding pressure, but then I'd be seeing some other symptoms, wouldn't I? Like coolant spewing out the cap?