My buddy's got an '86 F150 XLT Lariat and we're having... not tons of problems, but one that's really jockin' me. He's getting about 9mpg. He has what I call a "feather-foot." When I drive that thing, I bomb down the street, I can't keep my foot out of it. I get better mileage than he does when I drive it though... It gets terrible mileage, idles a bit fast, runs really rich, backfires at high RPM in park/neutral... but it has no mixture screws. I haven't messed with it too much. The carb is apparently a rebuilt off-the-shelf holley, and it's a 4bbl. The Windsor in it is stock. I can slow it down with the fast idle screw, but I can't tune the mixture at all. Is it a computer controlled mixture? Could the choke be stuck? He hardly puts his foot into this thing, and just gets no mileage, and the performance is OK. It's got a 2.73 9" rear/C6. He drives delivery as well, so it is basically money in his pocket if I can get this thing tuned any better. Thanks for any info you guys have for me... =D I will be doing a full tune up (plugs, and everything). Will I be better off with a new distributor (DSII and oil coil) and a non-computer carburetor (if this is a comp controlled carb?) from an earlier model 351? I'm at a loss! I'm used to '65 and under cars/trucks (2 mustangs, '56 f100, '62 ranchero) Also, what's a good header for a 351W to give a little bit better breathing?

 

How old is the carb? Have you done a regular tune up?


Backfiring is often timing so I would check that first.

Then I would look at normal tune up stuff. Plugs, rotor cap, wires good etc.

Finally, you almost have to suspect the carb. Could be worn jets, bad accelerator pump, float level set too high and leaking fuel causing always too rich etc. Last person to rebuild it may have just messed it up.

I would look at plugs and see if they give a clue after I checked timing. With it backfiring, I still think timing may be it.

Good Luck,

Lee

 

I know the carb you speak of....throw it away. I cant promise mileage will get any better (9 sounds bout right) but any aftermarket 4bbl 600cfm or so will work lots better. A warning though, if you were to go with one of thoes cheap Avenger series Holleys make sure the no. on the choke tower ends in -2 ex.90680-2. I had troubles with the exact same swap. also make sure EGR plate isnt burned out on bottom side.
one other thing,EGRs can be tough to find, so you might want to try and locate one before you mess with it. I wound up getting an aftermarket intake. Wish I would have just done that in the first place. in the end was way easier.

 

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Has anyone swapped a T5 into an '80s F150? I think that would severely help with mileage. =D I'm going to do the most amazing tuneup I can do, try and stick a T5 in there, and see if the mileage hella goes up. It definitely should. =] We were also thinking about swapping to a 2 barrel intake, as this isn't a smoke 'em every time we hit the gas truck. We want a cruiser, that gets good mileage. We are buying an '83 f250 truck with a manual tranny, and I was thinking we could gut the pedals and clutch setup for the '86, and swap to a T5. What's a good 2bbl for a 351W? Thanks for the info.

Basically, here's everything in a nutshell:
2bbl intake/carb swap
T5 manual tranny
great tuneup

It's already got 2.73 gears. The mileage we're hoping for is high teens, 16-17. Possible?