I have a 4 barrel Rochester on my 350 ci. The trouble I am having is that when it idles it seems to load up and run rich. When you look down the carb you can see gas dripping from the primary nozzles. I have rebuilt it once bathing it in Chemtool for two days. Then cleaning with hot water then blowing dry with compressed air. Runs good part and full throttle but not idle. Have checked for vacuum leaks are none. Put hand over air horn engine runs smoother. JIM

 

It sounds like the fuel is too high in the bowl on that side of the carburetor. Recheck the needle/seat, the float level setting, and be sure that the float is neither leaking or dragging on the side of the bowl.

 

^^^This!

Did you replace the float when you rebuilt the carb? The cat **** that passes for today's gasoline will attack the plastic float, causing it to sink, which leads to flooding.

 

I replaced the float with a new one. I even set the float a little low so it wouldn't flood.
When I was putting it together I put a vacuum gauge on the incoming line and vacuum held with the float raised. JIM

 

Your hand over the air horn probably alters the air flow through the venturi enough to reduce the amount of excess fuel coming from the nozzles. It still sounds like there is too much fuel in the bowl. Increased air flow at part and full throttle will mask the problem. The needle/seat may perform differently under vacuum when compared to pressurized fuel. Recheck everything that could allow excess fuel in the bowl. If you can see fuel dripping from the nozzles at idle, you have found what is wrong. Now you need to find what is causing it.

 

Including the fuel pressure.

 

are there any air fuel mixture screws? im not familiar with that carb