Idle mixture screw does nothing?
 

I have an 84 fb with an OER 45mm side draft carb (Almost identical to weber dcoe, with a few minor differences) and it's been running really bad. Adjusting the idle mixture screws does absolutely nothing. They can be turned all the way in (gently) or turned out all the way and still idle the exact same? It has a hard time idling too. Any ideas how that could even happen? How could it even run with the mixture screw in all the way since that means nothing should be passing through it?

What's your set up is the engine ported fuel pump exhaust ignition ect

I chased all sorts of ghosts getting my set-up to idle. Kept fussing w the carb day after day... It turned out to be the ignition was not up to par. I installed an MSD6A on leading and the car now runs great. I have a Dellorto 48.

Street port, not sure on fuel pump, racing beat exhaust, stock ignition. But im just wondering how it could even idle if the screw is set all the way in? Shouldnt that close off all idle mixture flow so it shouldnt even run?

But i just dont understand how the screw does literally nothing. Closed/wide open still runs the same.

Basically, the idle mixture screw lets in a certain amount of volume of premixed air/fuel so the car can idle when not on the main circuit, correct? So if the screw is completely shut, how is it running?

I don't think your ignition is an issue I was running a 12a bp with stock ignition
Make sure the proper breathers on the engine and carb are caped off that would explain it I have no experience with webers or any side drabf carb I have a holly 600 on my bp but there is a breather I have caped off and one on the engine and the vac advance as well I took the cap off the carb one time and it wouldn't idle I hope this helps

there are two circuits in the car, the idle circuit, and the main circuit. the main circuit works from airflow in the venturi, as we know

the idle circuit works based on throttle position. there are a series of holes in the side of the venturi and when the throttle plate sits right above one of these holes it creates a lot pressure and it will pull the air/fuel mix from the idle jet into the engine.

the idle hole is the closest one to the engine, and it has the idle screw to be able to separately meter the amount of the air/fuel mixture from the idle jet.

the next holes are a series of transition holes, and these are not controlled by the idle screws

the problem is that if the throttle stop screw, which is incorrectly called the idle speed screw, is set too high, the engine will be idling on a transition hole instead of the idle hole, which will cause the idle mixture screws to be insensitive or do nothing.

in this instance any mixture change has to be done by changing the idle jet

I should just send my carb to you lol

(or the idle circuit could be plugged up...)

I would suggest posting pictures and showing us what you have/are adjusting.

I'm starting to think my ignition needed upgrading bc of running MSD blaster coils stock. Eitherway it turned out not being the carb. Once the ignition was good carb reacted exactly as it should and super easy to dial in.