I have a 51 ford f1 with a 302 & aod & the original 3:73 rear-Holley 4 bbl carb
I am getting 10-12 miles per gal,I thought that I would do better than that.
any help would be welcome,thanks Bob

That's actually pretty good. Your truck weighs over 6,000 lbs, and you have tall rear gears. Somewhere around 3.00-3.25 will give you a better gas mileage number, but will take away from your power range.

You could fine tune the Holley, with jets, springs, squirters, etc, but unless you love to tinker, and keep spending money on kits, it usually don't change the end results much.

Lastly,You may have the camshaft for a car in your 5.0, and need a bit more torque that the truck/RV cam would produce. Again, cost effectively, You would be spending money/ time to change something for very little results

Really depends how you drive it Bob. I'd guess with a 4 bbl you're doing pretty good - at least the way I drive.

My 48 with a flathead and the stock 2 bbl carb gets about 15 in mixed driving. I don't know how your timing is set but that's about all I can suggest to improve things.

fwiw: the 48 - 52 F1 truck weighs right around 3150 with a flathead V8 - a 302 is lighter.

How many revs are you pulling at your cruising speed Bob?
If its less than 2100/2200 then i'd look at the gearing - my '87 std cab longbox 5.0 with aod pulls about 1750/1800 at 100km/h 62mph (our speed limit) and i'd like to change the gearing from it's present 3.55 to something a little lower so that i'm closer to the torque range which should help with mileage.
I've done the "sixlitre" tuneup which helped and i've also fitted a hydrogen system which adds about 1-2 mpg on a trip ..... i like messing around with fuel/mileage systems so as far as cost effectiveness goes i'm out of pocket but i'll just describe it as my hobby so that'll justify that expense.
Best that i've had out of mine so far is 21 us mpg but that was on the flat at night with no load and driving it pretty sedately - lately my average has been about 16 - 18 on a trip and i just plain refuse to measure it around town anymore with gas being about $6.80/us gal.

Is it a constant 4bbl's open? Or does it only kick into 4 when you give it a heavy foot? That might be why your getting poor mileage too.

I have been accused of occasionally offering an opinion based on prejudice preconception unsubstancated emotional bias rather then facts but then I always thought that is what an opinion is.

Dump the Holley, nothing but trouble, get a Carter AFB or its bastard sister the Ederlbrock, around 625 cfm.

And as stated elsewhere and I quote “your truck has the aerodynamics of a 4 x 8 sheet of plywood!”

Yep, these trucks are like pushing a brick thru the wind....over 60 mph aerodynamics has a big effect on mileage.

Also, what size Holley? 600-650 cfm should be about right for a 302. Engine in good shape and in tune? Correct timing is essential as well....

With the O/D trans, the effective final ratio, even with the 3.73's will be in the mid 2's. Plenty low to create some kind of reasonable fuel mileage. And yes, an F1 with a 289/302 and a C4 tips the scales at 3000 pounds. The AOD is heavier than the C4, so that'll bring it back up close to Tim's flattie weight. I've never known Holley's to be economy minded, they're really more of a performance carb. To eek out better mpg's, you need some diagnostic equipment and fine tune that baby good, as mentioned above. Don't overlook the distributor advance curve and timing. That is critical for optimum mileage. Even with barn door aerodynamics, I would still expect 15-18 minimum from that combination with a proper tune.

Also look into the jetting of the carb,If It was me i would start with #68 primaries,#72 for the secondaries,Many overlook the jetting of Holleys,this is where you may gain some of that economy. curve the distributor,reset the timing,see where this leads to.I agree with Wayne 15-18 mpgs should be the norm

Before I tore my 50 F-1 apart (not the black stock truck in the avatar), it had an old 302, C6 and the original Dana 41 with the 3.73. Also had a typical off-the-shelf 4 barrel Holley like you can buy at Autozone, etc. It was truly a rough truck, and the speedo/odometer didn't even work. I was running RPM's as mentioned above. It honestly wasn't that bad. I wish I could tell you what kind of mileage I got, but I couldn't measure it. But from what I recall, it didn't seem to be too awful terrible. But then again, I was carrying a stick around with me to check the fuel level in the tank.

The idle circuit plays a large role in part throttle/light load applications. A little effort there can be very rewarding. The wrong size power valve can make a lot of difference also. Buy yourself a book, a vacuum gauge and an air/fuel ratio gauge (Innovate as one example), and start tinkering and you will be surprised at the results.

Unless of course you have a double pumper and drive like a p***** off teenager. Than that is pretty good mileage.

……………….or buy a AFB (carter/eldo) and live stress free forever!

I gotta agree with going edelbrock/afb over holley. not a fan of holleys for mpgs...

I dunno, I kinda think the Holley/Edelbrock thing is like saying a 300/6 trumps a 302. I`ve used them both and they have their merits.

True, someone that's good with holleys can do amazing things... For us mere mortals an afb is pretty foolproof.