New to me: 1986 F150 4spd 4WD

Ok, new to the forum....been reading some posts and am need of making some changes to my old F150. I had a 1980 F150 300 / 4spd / 4WD that ran very well. So, I use to doing a bit of tuning.

The "new" 1986 has 43K miles and is in pretty decent shape. the feedback 1v carb, distributor, airpump need to all go away. The performance is terrible and the motor just seems to be fighting itself to come to life.

Looking for some input on performance with economy (MPG) in mind also.

I am thinking of a simple replacement with a non-feedback 1v and DSII ignition. However, am open to suggestions on efi exhaust, small 2v carb, and different timing, etc.

Starting with a clean slate and an open mind. Any details on part numbers, schematics, adapters, distributors, etc would be great.

Was asked for some detail on the pick-up and intended use: Will be a daily driver with some light hauling / trailering / off-road use (it is a 1986 half ton ford, right?).......standard 4spd with a fairly tall 3.08 rear (pretty sure), factory dual shocks on the front, custom cab......nothing fancy.

Thanks for the help and the input,


Dr Jay

Well-known member
Welcome to this forum! My first suggestion is to consider your goals. Next I recommend deciding
on which systems and problems you will address. I have found the most information and early planning choices by using the search function at the bottom of these listings. I really enjoy seeing the seasoned members vehicle mods and choices. Detailed questions of how to accomplish goals or assembly seem to get quality feedback. General questions seem to go slower. I love where you are headed, but; need some details like, transmission, gear ratio, purpose of truck, ..... on and on.
I'd jump on the ignition first. No matter what way you wan to to go on a carb you will need rid of the TFI unit.

If I had that vehicle I'd use the DSII dist with a GM Module and TFI coil.

If Any part of your current Feedback system fails it gos to a fixed timing with NO timing advance at all.
That is most likely the cause of the engine not running well.


Well-known member

I own a 1986 F150 with the same engine. When purchased from the original owner, it ran poorly and returned 8-11 mpg. I chose to do a Duraspark retrofit and have been quite pleased for 5+ years. As 80broncoman stated, if anything is wrong with the feedback system, the ignition timing is locked PLUS the carburetor is directed by the computer to go to the rich mode... poor performance and awful gas mileage. [4 speed manual transmission with 3.08 limited slip differential]

I replaced the distributor with one from a 1982 [pre-computer], which I had recurved, so that the centrifugal advance did not come on too quickly. This is because I chose to eliminate the EGR system. Without the EGR, the engine will be prone to pinging. This can be handled by retarding the static [base] timing, but will also hurt performance and gas mileage. I did maintain the catalytic converters.

I was not able to put my hands on a Duraspark ignition box on the day the switch was made, but my friend had a MSD 6AL ignition box, so I used that. If I had it to do all over, I might use the GM module, as suggested by 80broncoman. It is less expensive and is easily obtained.

I replaced the feedback carburetor with a remanufactured Carter YF from a 1970 F-350 with the 300 engine. This carburetor is factory calibrated for conditions without EGR and was not constrained by emission regulations. I chose to go with a manual choke for simplicity.

I used sparkplugs from 1987 or newer [fuel injection] as they reach farther into the combustion chamber and set the gap @ .050".

Be sure and replace all vacuum lines.

This change resulted in a truck which starts easily, runs well and returns 16-22+ mpg.
Updated a little about vehicle use / details / is in the very first post, at the top of the string.

Thanks for the help, progress is steady......


Famous Member
1986F150six":j2ag8ney said:
I was not able to put my hands on a Duraspark ignition box on the day the switch was made, but my friend had a MSD 6AL ignition box, so I used that.......

This change resulted in a truck which starts easily, runs well and returns 16-22+ mpg.

Care to describe how and where you drive? I can get 19mpg with hubs locked if I'm going 55-65 on a flat highway.

How do you like the 6A. I've considered getting one for the benfit of multiple sparks at low RPM but I'm not sure there would be enough of an improvement over TFI to be worth the money.


Well-known member
I drive very conservatively. Normal weekly driving is urban with stop signs and 25, 35 and 45 mph streets. I average 16-17 mpg in Winter and 18+ mpg in Summer.

At 55-60 mph, the mileage jumps to 22+ mpg. With 3.08 gearing, the engine is turning 2000 RPMs @ 70 mph and ~1570 RPMs @ 55 mph. I short shift [rarely exceed 2000 RPMs; normally 1300-1750 RPMs] and drive like there is an egg between my foot and the gas pedal. I get into the next higher gear just as soon as possible without lugging the engine.

I used the MSD ignition box just because it was available. If I did it over again, I likely would use the Duraspark distributor with a GM 4 pin ignition module [cheap and easily available].


Famous Member
I take it you're running larger tires because 2000RPM at 1:1 with 3.08s and 31s is about 60 mph?

Regardless, MPG numbers like that make you wonder what a lowered 2wd '96 with a M5OD, 2.75 gears and 235/75s would get at 60mph on a highway in Kansas with a tail wind


Well-known member
I am running 215/75 X 15" tires, which are stock. My transmission is the manual O.D. with, I believe, 0.71:1 overdrive ratio.

My son's truck [1984 with feedback, manual O.D. and 2.47:1 differential] used to get an honest 24-26 mpg @ 60-65 mph. This was before we [here in the South] were introduced to gasohol.

It is still stock [feedback system], but the rear end was changed to 3.55 [speedometer recalibrated] and the highway mileage is now 21-22 mpg. The truck is more fun to drive with the 3.55 rear gears.