1979 stock 12a with 80k miles and stock Nikki. Recently rebuilt my carb to fix a non-running issue and replaced all my vac lines. Runs great now, I'm able to get the idle down to 900 with 18-20Hg. The throttle plate stop screw needed to be unscrewed so its no longer touching the throttle plate because it was pulling fuel through the main circuit.

So it seems to be operating on just the idle circuit now, but the idle mixture screw does nothing. I can turn it all the way lean and nothing happens. Any ideas?

 

Double and triple checked for vacuum leaks and there is none. I can turn it all the way lean or all the way rich and it has zero impact on how the engine is running.

 

Most likely the idle mix channel in the carb is plugged up.

 

Hey thanks for the reply. I'm 100% there are no blockages in the carb. I rebuilt it only a few weeks ago, everything was put into my sonic parts cleaner then also scrubbed with a tooth brush multiple times.

Which is why I'm so baffled as to what going on, I've never had a carb that this has happened to. Any other suggestions?

 

I agree with divin, i think you still have a blockage in the carb. Sometimes crud in carbs can be REALLY stubborn

Just out've curiosity, what did you have in your ultrasonic cleaner?

 

I use a diluted simple green solution. Between that and the heated tank it cuts through anything and it safe for most metals.

​​​​​​It just seems that if there was an issue/clog in the idle circuit, the car wouldn't be able to idle, and it idles fine at 850-900 albeit a little on the rich side.

Also when I give it a quick blip of throttle, it doesn't want to take the gas right away. There is almost a quick dead spot then it takes it.

 

I had the dead spot problem due to my accelerator pump. My original accelerator pump started leaking fuel so I used one from an earlier model carb rebuild kit since I had the rebuild kit on hand. the arm on it was a slight bit shorter I believe. I do remember there were visual differences. I just don't remember what they were. I replaced it with the correct year range accelerator pump and the problem was solved.