Well I am really kinda at a loss. Not for sure if this is all I will be able to get out of it.
Stock 305/350TH everything stock except for a new holley carb 600cfm. New plugs, wires, cap, rotor and oil change. Tires are at 35psi. Car runs great but I noticed yesterday that it really didn't want to idle. Car died on my a couple of times. Other than that it runs good. The car only gets 12-14mpg.

Is this all I will be able to get out of this thing? Think what ever is causing it to not want to idle that may be affecting mileage? Anyway hope someone has some ideas. Going to check plugs and see what they show.

Air Fuel mixture, and Timing should be checked. The 600 cfm doesn't seem to be too large for it though, May benefit from a primary Jet Change. See what your plugs have to say.

You may want to check the float level, even if it's a new carb. Do you know how to check it?? I've had to set the level on most new Holleys.
Also, check the idle mixture. If it's on the edge of where it should be, you may have to tweek it a bit with the idle mixture screws.

The O2 sensor may be giving you a problem also, and they are sometimes blamed for poor fuel milage.

are you runnin a vac./mech advance distributor??? :texas:

Well checked plugs, kinda brownish gold, or goldish brown!. Checked vacum and found a small vacum leak. Then reset the idle mixture and timing. Seems better now, we shall see what gas mileage is now. Also let ya know seems I had to unhook the vacum advance.

Sounds to be within Specs.

http://i300.photobucket.com/albums/nn18/coyoteon2/miss/reading_spark_plugs.jpg

I had a problem with my carb a couple years ago. A piece of trash had gotten into the fuel line and stuck between the needle and seat. As a result, the fuel bowl level rose and would flood the engine at idle. The good news here is that your 1406 is easy to work on. Removing the carb top to adjust the float level, get to the needle/seat or the jets takes only a few minutes.

As far as your MPG, I'd think 18 or more (highway) should be about right once everything's tuned up properly.

However I'd recommend either investing in a wide-band air/fuel meter (Changing the carb's needles, springs and jets is simple enough) or making a visit to a local chassis dyno for a MPG tune up. If you could get 18 MPG, that'd be a 20% reduction in fuel cost so payback should come quickly enough.

Good luck.

Widebands are the bomb. I have used mine on 10 different cars already. Carbed and EFI.

12-14 MPG highway or city? If city I'm jealous! My 78 probably doesn't get that on the highway. But then again the AC is always on and its hardly ever driven conservatively.

WHO drives conservatively. in the Big Apple?
Isn't that the Birth Place of ROAD RAGE ?