[Gaz64]

Unlikely to have secondary idle mixture screws missing.
First up, the engine would not idle, and there would be fuel stains at the side of the metering blocks where the screws would go.

So i would say you have a earlier 2 corner idle carb.

Being electric choke, I would look at the fast idle cam falls down under the it's own weight, since if it flips back under acceleration etc, AND doesn't fall down, you get a higher than idle engine speed.

Also make sure the carb is even torqued, no thick gaskets etc.

Please check the front of the choke tower for the list number.

Gary