engine: was told 400m
trans: c6 auto

I picked her up yesterday and it is in great mechanical shape. even the gauges work ! not a lick of frame or cab rust. anyways it came with a 4 barrel carburetor (holly I believe) electric choke. unsure of the model. i was curious to know if i put a 2 barrel carb on it if I'll get better mpg? and if so is it really worth it or only a couple miles per gallon ? thanks for your time. new here.

 

Congratulations. Sounds nice. Post some pics. If you post your metal door tag, people will decode it for you.

If you already have the 4 barrel installed, I'd keep it. You'd have to change out the intake to switch to a 2 bbl and I doubt it is worth it. Your gearing might be a different story. There is a metal tag on the read end that can be decoded. it says what your gear ratio is. You can post a pic of that tag too.

What kind of driving will you do in it the majority of the time?

 

Yes Pic’s! Pics and more pics!

I could be wrong but I thought the 400/351M series of engines didn’t come in the trucks till 1977. If that is the case and you really have a 400 someone swapped the motor into your truck. Wonder if it’s a 390?

If you have a 4bbl on it I’d leave it on. It’s not gonna hurt your gas mileage. Our trucks where not known for they’re mileage to begin with. My 400 in my 77 had high mileage when I pulled it and it only got 8mpg and had a 2bbl on it. Truck now has a 460 in it.

Congrats on the new ride!

 

Welcome to FTE

If it has a 400, it was swapped in, first installed along w/the 351M in 1977 F100/350.

351M/400 valve covers have 8 bolts per side and were only available w/a 2V carb.

And, there's no such thing as a 400M, it's just plain 'ol 400.

Engine code is the 4th digit of the VIN - 1973/76 F100: A = 240 1V I-6 (1973/74) // B = 300 1V I-6 // G = 302 2V / H = 390 2V / J = 460 4V // M = 390 4V (1974/76) // Y = 360 2V

 

thanks for the replies, I'll get some more pics and what not once I get the canopy off and I'll double check the engine tomorrow based on information from the last reply. its gearing is 3.50 if what the last owner said was true !

 

after my vin check, the truck came with a 302 but after looking up the 400 I'm 99% sure it has been swapped with the 400. based on pictures and distributor location