Ive been trying to chase down a stumbling issue on my 79 F150 with a 300 with no success even after renewing most of the fuel and ignition systems.

For about 15+ years I had been running this truck with he ignition coil mounted on the inner fender, cant remember why I started doing this. At some point during some other work I moved it back to where the factory put it. Thinking back thats about when the problem started.
I decided to put it back on the fender just to see what happened and most of the stumbling went away. I still have a little bit but not as bad or frequent. A glancing search online showed a few other people with the same issue / fix.

Why would this make a difference (heat?) and what might I do to clear up that last bit of stumble.
Thanks

 

That is interesting.

Do you think it could be that the coil is oil-filled versus solid epoxy??

 

What brand coil? Ford mounted coils horizontally for a long time. They are supposed to have the terminals clocked at 3 and 9 o'clock position as when installed this way.

 

The one that is on there now has no brand marked, its blue with two numbers, 0816 and 1308 is definitely oil, the Standard FD-476 I swapped out sounds like it is as well, more oil than the installed one, it doesn't slosh as much when shook.

It was mounted horizontal on the engine and is now the fender well as well.

The Standard is the one that I had on the fender and moved to the engine before going to the " no name". I should swap it back in and see what happens.
It probably has a name I just dont have the box or receipt anymore from when I bought it.

 

I just went thru this on my truck, so some random thoughts for you...Did you replace the dizzy? if not and you have a spare or old one... A fresh start with timing can do some amazing things.. Also carb gasket and other vacuum gremlins, if you can run a vacuum test ... Also I was going crazy for a bit and wiggled my plug wires and found a plug that was nearly out of the socket..... and the ol'e plug wire that's not seated completely

 

I replaced the pickup coil /plate, i did pull the dizzy and I dont have a timing light. I set it with a vacuum gauge. It pulls good vacuum so Im not thinking a leak there. Carb gasket, thats something Ive not changed. I may take it to a "professional" and have the timing checked.
I did put the old coil back on with no change. But moving it to the fender has changed at what point it starts giving trouble, it was starting up at about 2 miles into my drive and now its more like 6. Its always started on a incline and pretty much continues the rest of the drive, up and down. I hadnt had much need to give it gas downhill until today, traffic, and it bucked on me a bit.

 

oh, and ive wiggles every wire on this truck while idling except for the taillight wires .

 

Carter YF carb?

Could be a float adjustment (incline bucking) or a loose carb baseplate to the body.

 

took it out and let it warm up then hit the carb and the vacuum line connections with starting fluid with no change in rpm.
Its a remaned Carter YF that I put on last year, the old one had the threads for the air cleaner mount stripped out. I went with the assumption that everything inside the carb is as it should be. Can you point me to a thread that shows where it should be so I can check on the float adjustment?

 

Could this be the problem....I hit the intake gasket with starting fluid and got a increase in RPM at the front. As far as I know its never been changed.

 

I had a problem all summer where my truck would shake when taking off in 2nd gear only after a hot restart. It ended up being a result of vapor lock. I put an electric fuel pump along with the stock mechanical pump and it's fine now. I read today's fuel boils much lower than the fuel these trucks ran years ago. Todays cars all have return lines to cool the fuel.

 

Yes, that could be another problem as you have a vacuum leak at the intake gasket.

As far as adjusting the float...tip the bowl upside down....the float should run parallel with the bowl.........make sure the needle valve is ok, too.

Float Level

 

OK, had the truck out today and it was hesitating as usual. Got just about home when it stalled out on me. this time it wasnt wanting to start right back up as it would the three other times its stalled out. While trying to start it I got some smoke coming out the dash. A bad sign, but a good sign in that I might know where to look to fix the problem. So here is a picture of the ignition plug with about 7 inches of browned resistance wire. and a bit of insulation missing at the plug.
The last week or so Ive been thinking thats its not been a hesitation a much as its felt like the truck has just stopped running but started it self back up.
What would be the way to see if this wire is the problem?
What is that other bit of wire there? it doesnt look like its part of the resistor wire, more like another wire that was there as well. The red wire in the same terminal looks good as new.

 

 

Are there any aftermarket add ons or accessories hanging off the wiring harness for a source of B+? Sometimes people will tap into the resistor or ballast circuit, that's not good. The switch itself or connections also may simply be corroded. High resistance in the grounds and connections roasts switches.