Hello guys I just joined today so go easy on me :P About a month ago I got a 1978 F100 with a 351m(not a great engine I know(will be swapping for a 351w in the next year or so)) It has the stock motorcraft 2150 that I had to rebuild.
The thing runs great, not burning oil or leaking anything and starts without pumping.This thing just has no low end torque, with it being a 351 and all I thought I could get a little squeak from a stand still(not even a brake stand).

Things I had to fix/replace: fuel pump, water pump, reset float on carb, fix vacc advance(the guy had it on the wrong vacc source), new plugs and dizzy cap/rotor, fuel filter.Still need a new airfilter(I don't think that could make a difference)
When I step on it hard from a stop I can hear the engine wind up but at soon as I get the pedal down all the way it kind of boggs down and I have no clue what this could be, I think it may be running lean(I have more power when the choke is not open all the way) I'll check the plugs tomarow because last time I checked they where a really light color(like brand new) When I got the truck the timing was set to 8* BTDC but valve cover says 10* so I advanced it to 12. Soooo might be problems: vacc advance need to be adjusted, timing , lean mixture ,airfilter,bad coil??? idk lol. If any of you guys could give me some pointers I'd appreciate it !
sean

 

You might fix that bog with a jet or float level change, but you'll not be lighting the tires.

As new, you had 257 ft/lb of torque at 1800 rpm. A nice number, but not enough to spin the tires on dry pavement.

Nurse it along, and plan your replacement engine/trans.

If you want more of a firebreather, you can convert it or replace it with a 400. A few of the right parts and mods there will give you 300 + HP easily. Many examples on this forum.

If you are set on the W, that's fine, but if you are putting a stock, older W in there, don't expect rockets to go off.

 

I wouldn't bother with it or the 351W. Get a 400 crank for your M and TMI's pistons, go from there.

 

Check the fuel filter. You can improve the low end with a new timing chain, installed 'straight up'. OEM cam timing was 4 degrees retarded, but you might want to wait until you replace the crank & pistons with 400 parts.

 

Best bet is if a rebuild or swap, go with a 400 crank and pistons (or 400 crank and 351C pistons and have rod ends bushed to fit). 351M and 400 share same block and rods, crank of a 400 has longer stroke and so pistons of 400 have the pin up higher closer to the tops so the piston tops aren't shoved into the heads.

In meantime, that Motorcraft carb might need a new accelerator pump diaphram or kit, and the thing about the timing gear is a good idea, except it is a bit of a hassle getting to it. The aftermarket lower timing gear that's on the crank often has three keyways, one is straight up and that's what you want. Time to do that and the timing chain would have been while the water pump was off.

You'll fit a 429 / 460 in there easier than a 351W unless you plan on a transmission swap too .... different pattern.

No way you gonna bark the tires though with a 8.0:1 CR 351M / auto so there's no need to abuse the truck trying ... but it's your truck.

 

i have a 78 f 150 with the 351m, and i was having the same problem (stalls when you lay into it) the choke setup was removed from mine, so i found an old 2150 in a junkyard and pulled the choke assy. off, and changed the power valve and acc pump and it took care of all the problems, now it runs and idles great. i can shove it to the floor off idle and spin the tires great, but mine is a longbed with i think 235/75s.

basically i would make sure the carb is set right, if it runs better once it's warmed up with the choke closed off a bit, then try adjusting it more to the rich side, i had to set mine as far rich as it would go.. 8:1 comp ratio i guess