I have been pulling my hair out trying to figure out the idle issue on this 68 I'm working on. I finally swapped the one from my 60 to the 58...voila! It runs perfectly with the known good carb. I pulled the top off the Carter and it looks fine...I even double/triple checked the gaskets under the carb itself. Where else in the carb could I have a vacuum leak?? It is bad enough that the car will barely idle when warm, and it will not idle when cold without major choke. I am not a Carter guy, so my knowledge is very limited. It is a fresh rebuild, too.
Adam, The idle air bleeds are probably clogged with some sort of debris. Remove the front venturi's & blow out EVERY hole. Then blow through the passages in the carb. where the venturi's attach. I had one one time where a piece of red rag fuzz was blocking the idle tube. Tom T.
Will that emulate a vacuum leak, though? I can smother the carb and the idle will improve dramatically.
Tom may be correct, since smothering simulates choking and drawing fuel from the main circuit, causing the engine to idle better. Besides blowing air, try cleaning the idle tube and air bleed with fine wire, like a twist-tie if you don't have a wire drill index. Check out the pictures to pinpoint the idle circuit passages.
