Lazy Throttle

[napa68]

Just some random thoughts......

You should establish a baseline with the harmonic balancer to ensure it has not slipped. If it has, most anything you try will be pointless unless you know where your timing REALLY is. I am a big advocate of having 36-38 degrees all in (initial and mechanical timing, don't worry about the vacuum can in this number) if your gasoline will tolerate it.

It could be carb related. Reading your description, it could be very rich. The cold engine hides that. These carbs are old and have been through more heat cycles that you can imagine. Eric Jackson just finished a carb for me where a float bowl was out .090. He did 2 others for me this year where the metering blocks were too warped to do anything with(and they were dead fat at an idle). Are the idle mixture screws responsive?

Does it smell rich? Does jacking the timing (beyond what your timing light is telling you) minimize the problem?

It can be frustrating, but can be diagnosed. It's a process. The more info you can provide, the better.