Classic/Antique Car Repair: 65 Caddy Rough Idle, crane fireball ignition, manifold gaskets

Question
My 65 Caddy has a rough idle and I think the Choke heat tube may be the culprit, but I need to find out.

So far with my 65 Caddy with the 429, I rebuilt the carb 2 times and ended up getting a rebuilt carb as the rebuilding didn't make a difference.  The plugs, wires, dizzy cap and rotor have all been replaced.  I even got a Crane Fireball Ignition to replace points and condenser.

All to get rid of a rough idle.  Still nothing worked.

I have closed all vacuum lines leading to the carb and manifold and even replaced the intake manifold gaskets.

But I still have a rough idle...

I know that the choke heat tube in the manifold is rusted.

Could this be causing the rough idle?  Also the primary bores of the carb (Rochester 4GC) have something called a "Vapor Vent Passage" on the gasket between the Throttle Body to Base Gasket...The Secondaries have it as well however I assume all is correct.

Even the "rebuilt" carb has these "Vapor Vent Passages."  

I dunno, I am at wits end.

Is it the Broken Choke Heat Tube or the Vapor Vent passages on the carb?????  Is it something else I am evre looking?

Please help as I really hate this rough idle...

Answer
It's really tough to hear about when people spend gobs of money and time on a problem, and don't get to a solution.

The first thing I would do is a simple test:  Take the air cleaner off, start the engine and let it warm up.  Now, take a sheet of cardboard, and SLoooooowly slide it over the top of the carburetor, flat on the top edge of the carburetor, so as to start blocking the air flow. Start from the front.  Listen to the engine as you do this.  If at ANY time while you are sliding the cardboard across the carburetor, you hear the engine speed up, you have a vacuum leak!  If this is the case, get back to me and I'll try to help you find it.  If it is not the case, (the engine simply slows down and finally stalls), you need to do a compression test on the engine - you may have a burned valve or some other problem.   

I doubt very much that the heat tube is the problem - because it only feeds the thermostatic control - even if it were totally blown out, it would only affect the operation of the automatic choke, not the warm idle.

Get back to me by using the "post a follow-up question" link.

I'll be here,

Dick