Hi guys! It's a mallory hei distributor. I tried both, ported vacuum and manifold vacuum. Manifold works best, but it didn't cure the problem. The secondary spring tension was the first thing I thought about too. I tried everything from very loose to very hard. The stuttering seemed to be a little less intense with the hardest spring tension.
The theory with the secondary wells not drilled seems more and more plausible.
What do you think about this test?:
In case there is something wrong with the secondaries, I could keep them from operating using some duct tape and tape them shut. Now the qjet should work like a 2bbl carb. If the stuttering at wot is gone, its obvious there is a fuel delivery problem that causes the engine to run lean.