Im pretty sure Autozone sells choke parts.

 

called them. they looked it up, they cant even order choke parts for that carb...

 

Is the choke flap stuck open or partially closed?
You can get most choke parts, try NAPA
Most of the time a choke just needs a good cleaning to get it working again.
Some common things that can affect MPG:
Timing
Timing Chain Stretch
Air Cleaner Element
Choke not opening all the way
Cam lobes worn from running low zinc oil
Leaking or burned valves (use vac. gauge or check compression)
EGR bad
Air fuel mixture (too lean or too rich)
Vacuum leaks
Air pressure in tires
less MPG from ethanol

I would work through this list............hope this helps!!!

 

You are averaging 19 mpg out of a 400 in a '78 4x4? What size tires are you running?

 

I rebuilt mt 77 F150 with a 300 I6, ALL stock with the original carb. I had to rebuild the carb, but constantly had to deal with a rich fuel condition which could not be fixed. I got another rebuild kit, and found the rich/lean air mixture screw was broken off in the carb as it was screwed all the way in.

A friend of mine who has a surplus business, bought a skid of stuff from a few Napa stores, and one of the items was a Carter 1bbl for a 77 Ford. I put the carb on and it ran like a new truck, but quickly (5-10 mi) ran very ruff. I got a rebuild kit and found the carb was off a 80 86 Mustang, MOntego, and a truck.

The kit for the carb cost $38, compared to the $18-20 for the original carb. The new carb had never been on a vehicle and was in the original box, but had set on the shelf for a decade or two. After it was taken apart, it was learned the float was out of adjustment.

The truck runs like a new truck, and it has a C4 tranny with 2.75 rear gears. It has stock sized P235/75R15 tires, on stock steel rims, open bed (no cap, or tonneau cover).

When I first got the truck, and right after the rebuild, I got 10 to 13.5 mpg. With the new carb, rebuilt, and fine tuned at my buddies shop we put it on the scope, and now get 19.5 mpg.

Most of my driving is on local roads, (25-55 mph), today I had it out on the interstate, and was running at 65 mph, or so, and it ran like a champ!

I would do a compression test, and get a vacuum guage, and timing light, rebuild the carb, or get a comparable replacement and fine tune the 300. It is a great motor, and worthy of the effort, and investment before throwing in the towel.

If you need any additional assistance, or pictures etc, please let me know. Also fmc400 knows alot about carbs, and may chime in, and if not look him up on here, he will lend a hand. Lastly, best of luck with your truck, you will enjoy working through it, and the feeling of accomplishment will make it all worth while in the end.

 

there are adaptors made by places like clifford performance tat make adaptors to run 2 barrel carbs, but i don't see how it would gain much, as it still has to breath through the tiny opening in the stock log manifold, if you had the intake machined down to mount a smaller 2100 it might solve some problems, but the 300 just flat out has breathing problems. i think that the adaptors are a poor fix.

I know that some people have got the 4 bbl manifolds and run 500cfm edelbrocks with good results (since in normal driving its only a 250cfm), and could easily be money well spent if you toss in some efi manifolds.

however if you were going to spend that kind of money, but not specifically looking for high-performance, I would put TBI on it. (but im kinda a techno-geek, even if the only transistors my falcon has are in the radio...)

 

That is quite a list! The choke is always in the fully open position. That explains why it does not want to start when I turn the key, and why I smell gas at startup.

Its funny you should mention the EGR. All the vacuum lines coming off the carb with the exception of the pvc and vacuum advance are cut off and plugged. So the EGR system is not working at all probably. People have told me that it is a bad idea to bypass the EGR or remove it. Not sure the reasoning behind this, I would think clean air would be better than dirty air??

I ordered the rebuild kit online from autozone last night (only $12.99). My girlfriend loves my truck, so I better keep it...lol.

 

The engine's ignition is curved to burn the EGR air and would detonate if you removed it without retarding the timing and/or richening the fuel mixture (got said detonation on a 79' Chevy truck one time after removing the EGR, sorta surprised me), plus the EGR actually cools combustion chambers a bit to prevent NOX.

EGR Systems - how it works

 

also, since the exhaust has already been through combustion it doesn't burn, so its kinda the opposite of turbocharging. getting a big engine to act like a small one while under low power

 

I get about 18mpg on my 77 F150 300 with 3spd with 31x12.5x15's but with the 215 70 15's i got about 22mpg

 

They are aprox 35s, with a 4" lif as well. I dont romp on it when im taking into consideration gas mileage, so this excludes gas spent trailing or mudding. Also it isnt all tune or pushing monster horse power the only after market would be intake and carb.

Boomer

 

EGR not hooked up might be part of the problem. The stock engine will run too lean and MPG will suffer. If an engine is too lean or too rich it uses more fuel.
The EGR keeps the combustion temps much lower and more important, ballances the lean carb mixture.
When you disconnect the EGR your fuel air mix will be way too lean and can cause burned valves, overheat your pistons and make your engine want to run on when you cut the key off.
The stock distributor is advanced internally for the EGR and will not work well without the EGR hooked up.

For the 300 six to work without the EGR you must change the following

Carburetor, even if you put the largest jets made, they are not enough to compensate for the huge air bleeds in the EGR carb design.

Distributor, must reduce internal mechanical advance.

Personally I have run both ways and now I would hook back up the EGR if possible. That might be difficult to get the EGR working but I would bet your truck would run much better, more power, more MPG and better idle.

 

That has to be some kind of record. I've never heard of anyone getting 19mpg with a 400 no matter how it's configured, let alone one on 35s with a 4" lift. I know you'll stand by your statement... but I remain skeptical. If all it took was a carb and intake and a light touch on the gas, I would think there'd be lots of people here able to duplicate it. The best I've seen is 16 maybe 17mpg from a similar truck.

 

I didnt do any of the "performance" upgrades myself, and I could be missing something in the mod but from my exp. and knowledge that is all that I can tell has been modded. I was shocked also to get this much but also happy with it, especially when I was moving (about a 1400 mile trip) to drive it to where I am currently located. Maybe it is a miracle of the sort, but i dont believe I have that kind of luck.

Boomer

 

Since bigger tires throw off the speedo and odometer (my 33''s throw it off about 5 mph 60 is really 65) then you arent traveling as many miles as the odometer indicates and hence, not really getting that kind of mileage. All other things being equal (a big if), the 300 should always get better mileage than a 400.