I have a 1976 F350 crew cab with a 460. It has the C6 and 59,000 original miles. Last summer, I started having a problem when it was hot outside and the truck had been driven for quite a while. It would start missing at cruising speed then I couldn't accelerate. If I tried it would miss and backfire out the exhaust. I could idle it home or gain a little speed feathering the throttle. It was very intermittant and I tried testing different things but nothing showed an issue.
I replaced the fuel pump and tested it to be a constant 6PSI. All the fuel lines are only 2 years old. Fuel filter is new.
I replaced the coil as it seemed really hot when the truck was acting up.
I replaced the 36 year old distributor to rule out the pickup. This made a positive difference in how smooth it ran. Timing is set to 12 degrees.
The plugs are new as are the cap, rotor and plug wires.

This spring, I started driving the truck and it has been working great except for the POS 4350 carb. A couple weeks ago, I replaced the carb with a new Edelbrock 600. The truck has been running awesome! It has good power, idles very smooth, reasonable mileage. (LOL!)

That is until this morning. Driving to work it acted up again. I limped it back home. It is only 0 C here this morning! Before the issue only showed up when it was hot outside and the truck had been ran for quite some time. Now it acted up when it is cold out and the engine had just gotten up to operating temp.

Anyone have some ideas? Ignition module maybe? A lot of the parts I replaced I wanted to anyway since they are pretty cheap. When I bought this truck, I believe it was all original. The plug wires even had 1976 on them!

 

Same thing happened to me, I believe it was because the carburetor flooded. Has your truck sat for any long periods of time? It probably sucked up some junk out of the gas tank. Take the airhorn off your carb, edelbrocks are about as simple as they get, and see if theres any dirt and stuff clogging ports and holes.

 

I've been using the truck every day for the past 3 weeks and it has been working great. I used it last night with no issues.
It may be the carb but since this seems to be a similar issue as when I had the old carb installed, I'm not so sure.
I'll pop the top off and give it a look. It really seems to be something in the ignition though. Of course, I could be wrong.

 

Also the Edelbrock carbs don't like much fuel pressure. I don't know the max but I seem to recall 4psi or so. 6 might be too high and over powering the float valve.

 

I checked the fuel pressure and it is a constant 6PSI.

 

Well Edelbrock tech Q&A says max is 6.5, with 5.5 being optimum so I guess you are within spec. Maybe choke? Next time it does this pull over right away and take the top cover off the air cleaner and see if it is wide open.

 

I checked the choke and it was fully open. Once I limped it home, I pulled the fuel line off the carb and it was full of fuel as it sprayed out (I wrapped it with a rag before removing). I quickly popped the fuel gauge on and it had good pressure too.

 

Well, popping out exhaust can be a rich condition, popping out the intake is lean. Not a sure thing that you are rich, but that is one cause. I have seen that ignition module or the "box" do this. It was not a bad box though. It was a bad plug connection on the box, check the plugs and slightly bend the blades to make a solid connection.

 

This is what I figured to. Since it is not popping out the carb, it should be getting enough fuel. If it is not firing right, that may cause the rich condition.
I will check the connections tonight. Thanks for the advise. I am also going to check the resistance of all the wires running from the box to the coil and distributor. Maybe I have a break somewhere? I checked the harness when I was putting the truck back together but it's condition may have changed in the last 3 years.
While thinking about this, the last couple days the truck seems to start more so when I release the key as opposed to when it is cranking. Maybe my ignition switch is going south too or could the box / connections cause this as well?

The reason I keep thinking this is ignition related is I was having a similar issue before I replaced the carb.

 

Try taking the plugs out when it does it. See what they are looking like.

 

I was getting very bad backfire. like a flame thrower out the tail pipe! My truck would shut off so when i tried turning it over it would just back fire and sometimes start back up. I replaced the ignition module and coil and starts right up. no problem what so ever anymore.

 

Sounds like an ignition module. Try that first. I have also had the reluctor in the distributor do this to me in the past. Poorly remanufactured with too much gap. Hope this helps.

 

I did some troubleshooting last night. Wires check out fine, voltage is good, coil is good.
I tried to test the stator but found the resistance was jumping around. Popped the cap off the distributor and see the reluctor is hitting the stator! As it advances, it contacts it even more!
Looks like this may be my issue. As the carb opens up, the vacuum advance moves the stator which gets knocked around even more by the reluctor.

I will exchange the distributor for another one since I only installed it 1 month ago and give it a try.

 

Glad you found something wrong; so to speak! Sounds like things will return to normal soon!! Congrats.

 

Thanks for the congrats but the one thing I have learned while working on my truck is not to pat myself on the back too soon. I've had times where many small things were contributing to one problem. Just when I thought I had the problem licked, my truck would do it's best to prove me wrong!