How far on a gallon?

I've tested numerous Panteras, and 12-14 MPG (US) is not uncommon. Running over 100 MPH for hours on end in Bob Benson's car returned something like 12 MPG.

Check for leaks in fuel lines, among the usual carb issues.

When I picked up 6328 this last January, with its' fairly stock 351 w/Edelbrock Performer and Holly 670 Avenger, I drove 620 miles to get her home. I was cruising at about 80-85 most of the way and got 18.5 mpg US. Was totally amazed.

Thanks for the response guys.
The Holley is a new 1850S/4160 with a conversion kit for real secondary jets. I'm running 64 primary and 66 (or was it 68?) secondaries. The new carb replaces an old 700cfm Holley (a 4778-2) - I replaced that because it was getting only 10mpgUK/8.33mpgUS. Ignition timing is correct (Mallory dual point) and there are no obvious leaks or fuel fumes coming from the engine bay. The rolling road guy was happy with the mixture. From reading the other posts here I seem to have the worst fuel consumption for a stock (almost) car. I get 12mpg (10US) on country roads, and 12.9mpg (10.75US woopee!) on a motorway cruise at a steady 70mph.
Could it be the cam? (I have no idea whats in there!) Any other ideas?

Start with your plugs. Pull them to see what color the tips are: tan, black, oils or fuel soaked. There are sites that can help match the color of the plugs to a healthy engine. This helps narrow down the problems.

Next, try a compression test to make sure everything is sealing. Leak down test would be better but more expensive. If your rings or valve seats are shot, no carb tuning would help.

Look for any vacumn line leaks. Spray vac lines with carb cleaner or penetrating oil with the engine running, if the engine increases RPM you have a leak. Do not forget the massive vac line that runs from the engine to the brake booster up front in the trunk (boot).

If those check out, then comes the fun of carb tuning. Get a good holley book and try jet and vac value combo's. A few jet sizes can make a real difference in both performance and ecomony.

This is all trial and error stuff, so perhaps you can tap a friend who knows these things to speed up progress.

I have a '74 with between 400 and 450hp that gets 15mpg no matter how far my foot is buried into the carb.

I also have an'86 GT5-S with a stock 20k mile motor that gets 10mpg no matter how far my foot is out of the carb.

Go figure.

Michael

I have a 73L & on the old low compression engine it had in it when I purchased it I got 19 mpg on my last long trip (1350 mi.) My rebuilt engine I have in it now- approx. 425 FWHP- is giving me about 15-16 mpg. A lot better performance now though, so I'm happy to give up a few mpg!

I have a Holly 750 double pumper, motor built 30 over, 400 HP, 6 MPH.

Hey Cozman,
I would be terribly unhappy if I had all that ond could only go 6 MPH. Maybe you meant MPG?

If you're running unleaded fuel, the plugs are not a indicator of fuel mixture as the unleaded fuel does not give the plugs color. It could however show oil fouling or excessive fuel "drowning"