Holley Idle mixture screws non responsive?

How far are your mixture screws adjusted right now? Re set them to 1 turn out from the seated position.

I may not be reading it clearly but I hope you are not saying that you set the initial timing at 16 with the advance unhooked then when you plug it in it jumps to 38?

Another thing to check…. Being that it is a new carb. Do you have all the unused ports plugged?

A 750 should just drop on that engine and run in my opinion. The problems are probably coming from other related issues.

In other words… I think you may be trying to adjust the carb to cover another issue.