I have been working on cars with carbs for years. I have rebuilt my share of them. The truck was running fine one minute, then way too rich at idle, wont stay running unless I give it some air via the pedal. I looked down the throat while idling fast and there is fuel dripping from the ring where fuel is siphened into the carb for operation. It is supposed to be bone dry up there. I checked the float adjustment and it looks good. I dont know where to look in the idle circuit to track where this overflow is coming from. I can tell you this, there is a lot of turbulence in the sight glass where the floats are.

 

Stock carb or Weber?

 

This carb is less than a year old. It is an aftermarket car I bought on ebay. It was running great, then all of the sudden wont idle, so I checked it out and as I said before, fuel is dripping onto the top of the primary butterfly through the ring that feeds the fuel under load. Ive looked at diagrams of the idle circuit , maybe Im missing something. I have been wrenching a very long time and know American carbs pretty well, Ive owned this truck a long time and this is the first time Ive had problems

 

I forgot to mention that it will return to running fine now and then. It will idle so smooth that you cant tell its running, then all of the sudden, same crap black smoke out the back at idle and hard to keep running. Throttle response is better than ever though

 

What brand/model carb and are you using the stock fuel pump?

 

it's an factory replacement, stock carb. The fuel pump is a Cardone, it's new also. and stock replacement

 

OK you mentioned American carbs so I was just verifying. That eliminates a few things I was thinking.
Other thoughts . . . some thing/passage has to be open to allow the fuel to vent out like that.
Is there a gasket or seal or plug that may have become damaged to cause this?
Or
Did some "dirt" break loose and jam open a passage where a check valve/ball is?

You don't know the history of this particular carb so it could be something not caught by the rebuilder.

 

Came across this while looking for something else
https://www.yotatech.com/forums/f116...p-carb-211651/