Classic/Antique Car Repair: 66 Galaxie rolling/rough idle, chuff chuff, fuel mixture

Question
Dick,
I recently purchased a 1966 Ford Galaxie, 390 2bbl, that had been well-maintained by previous owner. After buying it, took it to a local mechanic to have it checked for leaks, etc., which there were a few of, but it was fixed and tuned up and returned.
It ran fine for a weekend, and then a few days later the car started fine, but had a hard time idling when warm. The idle surges, runs rough, sometimes stalls, but it runs fine under acceleration. Had the carb fuel mixture adjusted and idle speed dialed in. The car ran great--started on the first turn of the key the next day. Then when I started it again later that day, the idle was rough and it died at every light. I had to drive with both feet to keep it running. The next day it started fine, ran great the first trip. Later that day, idle is rough, rolling, low rpms, etc. This car has had a tune up, adjustments, a carb rebuild, new distributor, plugs, wires, coil, fuel lines, etc., all within the last year. The previous owner rebuilt or replaced everything attached to the block.
I'm at a loss. Where can I go from here?  

Answer
Intermittent problems like this are very difficult to track down.  You can keep throwing money at the problem in hopes of fixing the right thing, or you can get it into the hands of someone who has an engine analyzer, and who will spend the time to keep on it until he spots whatever is fouling up.  There is no magic cure, I'm afraid

I can think of about 20 different things that could cause the symptoms you're having, the most likely thing being that the needle valve is sticking in the carburetor, but it is going to take a real mechanic to prove it.

Just for a couple of examples:
If, when you have the bad running, you can get someone to run around in back of the car and report on what is coming out of the tailpipe, (both sound and content of the exhaust), it will help a lot. If you see black sooty exhaust, it is most likely the needle valve, but if you hear a chuff-chuff-chuff sound from the exhaust, but the emmissions are normal, then you have a sticking exhaust valve, which is a much more serious problem.

I wish I could be more help, but you really need a good mechanic to get interested in this problem, one with experience and good equipment, and a generous heart!

Dick