Do you think it is worth pulling and checking that? I’m going through my timing excises after i eat some turkey. The bouncing vacuum gauge really adds some validity to Mark’s comments above about timing or a miss. I need to investigate that. I always assumed it was just carburetor issues. The surge is gone and now the idle mixture screws are responsive now. Being new at this, I’m not sure how “responsive” the idle mixture screws should be.
If it is worth pulling the carb, what is that procedure called, so i can google? “Secondary stop screw adjustment”?
Edit : I think mine may be good. I just watched the Holley how to and it said don’t touch this adjustment unless you have a big cam with low vacuum. It said to verify the flaps cover the groove and when I had if off yesterday, I did see that the vertical groove was not visible when the flap was closed. I adjusted the primaries to have the square and saw the secondaries didn’t have a visible groove at all when closed. You can kind of see it in the pic below.
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From what I can see in the pic, your secondaries appear to be closed all the way. Others are correct that ordinarily you would not need to adjust this screw as it would be set correctly from the factory. However, in my case, I bought a used carb and someone had monkeyed with it, so I had to readjust back to spec after experiencing similar idle issues on my 460.
Timing and potential vacuum leaks should always be addressed first before trying to tune a carb.
Both my 750 and 650 Holleys are sensitive to idle screw adjustment +/- 1/8 turn when you are near the ideal setting. The idle air bleeds are particularly sensitive to clogging, especially with poorly maintained K&N filters. In cases where I've had difficulty maintaining proper idle, I've removed both screws and used my rubber tipped blow gun to give each screw port a quick shot of air, and also do that to the air bleeds.