340 fuel/ignition issue?

Bewy said

[1] Make sure the base gasket seals all the passages in the carb base. A leak here causes strange things.
[2] Make sure the choke blade is vertical, not flapping around, engine running.
[3] Make sure the sec air valve dashpot is working; should pull in with engine idling. With engine idling, make sure the connecting rod from dashpot to AV moves freely.
[4] Engine off. Push in dashpot plunger & release it. Compare to the other carb. If it is slow, the diaphragm has gone hard, causes a rich mixture.
[5] Make sure the AV moves freely. Should be at 2 turns as a starting point.

Keep us posted!

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Thanks, Bewy,
Re: #3, To clarify, this sets the AV drop, and you are saying to check that there is a bit of wiggle/looseness so there is some drop set?? (It was set at maybe .020" but I increased it a bit.)

[1] Haven't dismantled it to check the base gasket yet, or to check for debris in needle seats, but will soon.
[2] No choke
[3] Both dashpots are new. Activates easily with MityVac at only 5 in/hg. It does release just a wee bit slower than the one on the previous 6518, but does seem to release fine, smoothly.
[5] AV does move freely, was set at 1-1/2, and I was not getting any bog in the bit of driving before the problem.