77 F-150 with a 351W. It runs smooth then suddenly runs rough with no power and backfires through the exhaust. I have replaced the carb and all connected, distrubutor, plugs, wires, breather, vacuum hoses, fuel lines and filters. It will run smooth and then rough, then smooth with no particular pattern. It does the same thing either driving or sitting. What else could it be?

 

Here's a thought, could it be a fuel pick-up problem. Maybe trash in your tank? I had a miss problem with my 351M. It would run fine cold but miss when it got warmed up. Turns out it needed a tune up (bad condenser). A few people thought maybe I had trash floating around in my tank since my truck is a 74 model year. A tank that old could have alot of dirt in it. Anthow it's just a thought. Good luck.
Mark

 

Have you checked your timeing?I have a 80 f250 with a 351m that did the same thing.Bring any cylinder up to tdc then turn the crank backwards and watch your rotor when your rotor starts to move stop and look at your timeing marks. If the crank moved more than 7 degrees your timeing chain is shot or (or it might have allready jumped). Good Luck (Did you triple check your fireing order on your plug wires)

 

get ya some carb cleaner and go around the intake maoifold, carb, and anything that sticks out. I just did battle with one of those

 

part two..............look for a vacuum leak

 

all of the above is certainly good advice, if all else fails try to check your oil pressure gauge as the problem is occurring. Mine was doing the same thing, turns out the oil pump was seizing and the distributor gear pin was bending causing a timing backfire. I had noticed a needle fluctuation on my oil gauge but figured it was just the sending unit. WRONG!!!! Jim....

 

Hey man, I have been having the same problems for about a week or so. I changed the distributer and all that too. But on mine, when you unhooked the vacum advance, it ran a little better. Is that the case? If so you might want to trace your wires down from your distributer to your ignition box on the fender well. because when i did my wires were brittle and some of the coating came off and they grounded together and it ran horrible. Unhook your vacum advance and see what happens. let me know if that's what's wrong

Mitch from Texas

Crane510(No Email Addresses In Posts!)

 

Hey man, I have been having the same problems for about a week or so. I changed the distributer and all that too. But on mine, when you unhooked the vacum advance, it ran a little better. Is that the case? If so you might want to trace your wires down from your distributer to your ignition box on the fender well. because when i did my wires were brittle and some of the coating came off and they grounded together and it ran horrible. Unhook your vacum advance and see what happens. let me know if that's what's wrong

Mitch from Texas

Crane510(No Email Addresses In Posts!)

 

 

It ended up being the ignition module after aeverything else. Now it runs great! Thanks!

 

It ended up being the ignition module believe it or not. A $20 part after all that.