Ok guys,
Help the 'ol moderator out here.

I just rebuilt the engine in my truck. It currently has 750 miles on it.

Specs:
1983 F-150 4x4
351w with a motorcraft 4100 4bbl. model for a '65 Fairlane GTA
8.7:1 compression
stock heads
cam is Summitt 4400 mild lift, short duration, "RV" cam."straight up"
c-6 automatic
3.50 gear in rear
ignition is points-type distributor with Pertronix Ignitor conversion
Dual exhaust with no cats and no cross-over
32 in B.F.G all-terrains
(pic in gallery)

My problem is I'm averaging about 8 mpg. This is unacceptable.
Is this normal?
This engine isn't working that hard. It runs very good. It has good power (much improved over the 302 it had).

Now, to complicate matters, the carb has no provision for vacuum. So I have run the vacuum line from the dist. to the manifold. I had slight pinging, so I backed the timing down.

If this mileage sounds about right with my set-up then fine, but it sure seems it should be more.

I have considered the MSD-6A and then add the timing adjust feature. But if it wont help me then I don't want to blow 250.00

I've also heard something about an adjustable vacuum device from Accel?

Do you think the problem could be in the timing? The carb? Or not at all and I'm chasing a pipe dream of at least 10-12 mpg?

I realize mileage should improve as the engine breaks in, but has anyone ever heard of gaining 2-4 mpg? I haven't.

Thanks guys,
Chuck

 

I think you would be better off with a newer type carb. A small 600cfm of some sort that you can actually get jets for and tune it. Plus it will have the vacuum ports. Who knows how that old carb is jetted.

Also, if you have the proper width rims for those tires, I would pump them up to the sidewall rating. It will ride a little rougher, but it should help the mileage.