Ok, here we go. I've got a 1977 F-250 4x4 that had a blown 400 in it. I just recently put a 400 out of a 78 in it. The problem is that it ran fine in the other truck but it runs like crap in mine. Starts hard, barely idles, misses like crazy with any kind of pedal. What could be wrong? I've replaced the cap, rotor, wires, and plugs to no avail. Gets a little better as it warms up but doesn't go completely away. I've noticed that the choke linkage is bound up a little so that it doesn't close completely but it does open all the way after the engine is warm. I don't have much more patience for this thing, I just want to fix what's wrong with it. My only other idea was the ignition module on the fender since that's the only thing that I haven't replaced yet. I hope someone can shed some light on this one for me.
My second question is, do I really need all these vacum lines?! Can't I just hook up the power brakes, tranny modulator, and accessory vacum to the tee on the back of the manifold. Hook up the advance to a port on the carb and do away with the rest of the junk? It's a real rat's nest with all the emissions stuff. My 92 Towncar doesn't have this many vacum lines on it! Yet again, I hope someone can give me a straight answer on this one. Any help would be GREATLY appreciated. Thanks in advance

Brady Archibald

 

Brady, I think your two questions may be related. Yes, you can get rid of all that vacuum plumbing like you described. I have done that on my 78 351M with good results. I had to go up 3 sizes on the carb jets, though.

I also think you may have a vacuum leak somewhere. Try running a vacuum line directly from the passenger side carb port (under the choke housing), directly to the distributor vacuum advance. See if this helps. This will bypass some of the warmup/emissions stuff. Make sure all the open vacuum ports on the manifold are plugged.

 

And just one more thing to check .. When you installed the motor did you hook up the ground straps that go to the motor from the firewall.

:-X23

 

Another suggestion: Check your Firing Order again. Did you install motor and then replace wires BEFORE starting the engine for the first time in it's new home? No insult to intelligence here, but you may have crossed a few wires. This could account for most of the symptoms you are having.

 

check your timing, my 1977 f250 has a 400 and it ran like crap till i rotated the rotor asembly to advance it a little, did wounders for me.

Deisel83