I have a 77 F150 4X4 with a 351M with a reman Motorcraft 2150 2V carb. A hissing sound got me to looking under the air cleaner base (aftermarket chrome base and lid with a filter inbetween). Found the leak. It was where the hot air stove pipe was supposed to be installed at the electric choke! No pipe found on the carb nor lying on top of the intake either. I couldn't even find where the pipe would have been attached to the intake to begin with. Looked around the carb and I noticed there's more vacuum ports plugged than in use. Looked at the heater hose to intake fitting vacuum tree. There is not a single vacuum hose attached. The vacuum pull off has no vac hose attached and the choke mechanism has a zip tie to prevent the choke from engaging. My brother came by with his 78 for me to look at. All his stuff is right where it should be, but also confirmed that I have missing parts (if mine is supposed to look just like his). His has a dash pot on the throttle side. Mine doesn't. His has the bolted on stove pipe right below the choke. Mine doesn't even provide for the bolt up on the intake for the stove pipe. If anyone out there can point me in the right direction for vacuum and emissions diagrams, under-hood stickers, or can give me the specs for what was actually on a 77 351M 2V I would be greatful. I can see what my brother's has but I don't even know what differences there might be between the 77 and 78 as far as emissions and choke set ups. I know what my carb doesn't have compared to a 78. I just don't know what mine is supposed to have as a 77!

 

this may be a reach, but i think those two years were pretty close . you mght just get some vacum hose of the right size ,' aprox 6 feet of it, and copy his . if you are missing external hard parts , you might go to the junk yard , i may be wrong but the heat riser should come from a small hole in the top of the exhuast manifold on the same side good luck,bob

 

Don't know if this may help. I have 1979 F100 302V8 2150 carb. I have a steel line attached by rubber hose to a vent on the air horn rear; the line then goes down to a bulge on the right exhaust manifold below cylinder #4. It attaches to bottom front of bulge. From top of bulge is another steel line that goes up and ends in a threaded fitting at the electric choke. Vacuum from the carb internally pulls on the choke housing. Air is pulled from air horn port down to the bulge (stove) and then up to the choke housing. If this path is connected; but blocked, the vacuum will cause a whistle or ringing in the choke as air is pulled from the shaft at rear of choke housing. This hot air stove must be clear from carb to stove to choke to work and assist the electric aspects of the choke. Had to clean the tubes and stove with rust blaster and stiff wire to get it to work.

 

Thanks Bob and Rainbow for the info. I'm slowly gaining knowledge about the differences in the 77-79 Trucks. From what I have found, there was progressively more EPA required emission junk added to these trucks in a real narrow span of time. Same thing concerning dropping cylinder compression rates. For anyone interested, I found vacuum diagrams listed for Ford trucks pertaining to all engines offered in trucks on the Autozone part store website. Just click your way through the site till you get to the diagrams. You can also print the drawings. Now I have to figure out what emission junk my truck actually had on it to begin with.