Rick, I tried more advance and nothing really changed, less advance made the car run like crap. The choke is definitely fully open after the engine has run for about 5 minutes.
CHANMADD, the firing order is correct 15426378. The engine runs fine and the car will just burn the tires if asked to do so.
Jac Mac, I will check the head gaskets but the fellow that put the engine together is a pro so I would be very surprised if he made that kind of error. I believe that I have the correct NGK plugs but I will check the number and indicate it here later.
lovehamr, I am not sure about the low speed advance. I have a stock Ford distributor with the vaccum advance disconnected and a Petronix module instead of points.
MOTORHEAD, the engine was rebuilt a couple of years ago but the heads were just changed this spring. The engine was using
oil through a couple of the old valve guides so instead of having the cast heads rebuilt, I went for a set of Edlebrock Street aluminum heads. The engine no longer uses any
oil. Total mileage on the engine is 5,000 miles since being rebuilt and 1,000 miles since the heads were changed. You ask if this is a new problem and I have to admit that I am not really sure. It runs well but I happened to pull a plug just to take a look and it was white so I started messing with it. It was at that time that I noticed how much gas it was using which was a complete contradiction of the plug color. Really bad gas mileage and white plugs don't make sense.
Once thing I forgot to mention earlier is that the idle speed changes by 50 or 100 rpm on occasion. This usually happens when the hot engine is restarted after sitting for a half hour, it will idle at 500 or 550 in drive instead of 600 rpm. The car has a C4 so a slight change in the idle speed is more noticable than with a manual transmission. I have also changed the power valve just in case that was the problem. Thanks guys.