i have a 1978 f150 shortbed 4x4. it has a 351m and is old.... i've been piecing this truck back together for about 6 months and need it going asap because the snow has hit and my wife needs her car back....haha
the truck starts right most days with only a couple pumps of the gas and idles fairly smooth. if i slowly push on the pedal, it will rev just fine and come back down to about 650 rpm on its own and idle smooth. if i hit the gas hard it dies out. i figure that its either getting too much air or gas and just dies. i drove the truck a couple days ago and it was just fine, which is unusual for this truck....
i put in a new fuel sending unit yesterday, and it started right up then, and today. i let it idle and warm up for about 15 mins to melt the snow drove it out of my apts and it dies. if i let go of the gas and let it idle, it idles but then sputters bad. if i hit the brakes or try to turn when it does this, it dies. it'll always start right back up, but will die continuously after unless i let it sit for a while. i dont know where to start, what to check, or what could be causing this.
the only thing that comes to my mind is either the vac advance on my dist. the electric choke, or other choke issue. there is also a continuous high pitch squeal while the engine is running, that i think is associated with a vacuum line.
any help or suggestions while my laundry list of questions would be a great help.

 

78,
you've most definitely got carb issues. Assuming the choke is working correctly, the stumble and die when you hit the gas sounds like the accelerator pump on the front of the carb going bad. What kind of choke do you have; electric, manual, stove heater? Is the choke open fully when the engine is warm and closed when starting? If it's not either of these positions you have a choke problem.


A vacuum leak shows up well when let idle...you'll have an erratic idle.

You can check for this by spraying carb/choke cleaner around the vacuum lines and carb slowly until you hear a surge in speed. I say slowly because you need to know where you sprayed to cause the engine surge. That will tell you where the hole is letting the spray into the carb.

 

X2 on that response.
Carb rebuild kits are cheap and easy to do too.

 

i've been tossing around the idea of rebuilding the carb, but i dont know how long it'd take. is this like a weekend project or what? my choke is a black circle about 2in in diameter and about 1in thick. on the face it has an arrow point clockwise with the word lean on it. i've adjusted it since my post and it has made a bit of difference after it backfired haha. it seems functioning because i can see the choke plate move while i twist it. there is also a wire that connects to it that runs into my wiring harness, but i've not been able to figure out what the wire does. checking it with a volt meter, it doesnt seem to be carrying a charge of any kind.

oh and from what i can see, there is very little movement of the choke plate between warm and starting. i was under there earlier and had seen the small c-clip that hold the rod connected to the choke plate was missing. it's been replaced as well.

 

Can be done in a day. All depends on how long you leave the carb to soak in the solvent really. There is s GREAT write up on how to do this. Lemme find it...

 

I cant figure out how to post a link on here!!

Anyway type this into google, it will be the first one that comes up: rebuilding motorcraft 2150

This is a step by step with pictures of how to do it. I had never rebuilt a carburetor before and this made it

super easy.

 

in a rebuild kit, i havent seen one yet thats really anything more than the seals and stuff. not new jets, floats, nothing. is that normal or do you guys know any good places online to get one? like maybe summitt racing, i havent checked there yet.

 

unless those items are completely shot, and I don't see how that can be, you won't need them. Just clean them up a bit and replace the seals.

 

awesome! thanks. that was the kind of stuff deterring me. parts i couldnt find or that were crazy expensive. are there any parts that are a good idea to replace or inspect that you can think of or i could find a list for? i really appreciate all your help.

 

78, I think the kit will have everything you need including a new spacer, the thick black gasket looking thing that goes between the carb and the intake manifold. This isolates the carb from engine heat and allows the fuel/air mixture more time to equilibrate.

Get a good kit. Mine was from Napa and had everything. The instructions have a parts breakdown showing everything on your carb. If you have trouble, do a google search on "autolite 2100" and then click the "Images" tab at the top. You'll find a schematic to save and print off as needed.

Check in here for help as needed too.

 

i got the kit and the carb all cleaned up, i'm doing the reassembly now. so far so good, a few of the guts were bad, stuck, gummed up, and the choke pull off was bad...haha i guess thats what happens with a totally original, i.e. 38 year old carb. its been interesting to see all the workings of it though.