BARDAWG85

79F150 6.6L 400 with new 4 barrel Holley carb and edlebrock intake, new Holley fuel pump(the blue one), new HEI distributor, new starter. I have good vacuum and good fuel pressure but as I get going down the road, it dies on me. I can get it to start and run just enough to get back home where it idles just fine in the driveway. I check timing after every time it dies because I had a bad distributor before but it's always good to go. I can't seem to figure it out. By the way, I'm in no way a mechanic it I can usually figure stuff out, so you might have to dumb it down for me. Thanks in advance for any help.

Braggs

What cfm is the carb? Maybe too big and chokes out/low vacuum? Put a vacuum guage on that you can watch while driving.

The symptoms remind me of another vehicle I had with a failing fuel pump. Ran all day in the driveway just fine but would die on the road 1 mile away from home every time. Could be vapor lock issue too. Once you get going the heat blows onto a fuel line? Just giving you ideas bc I don't really know.

BARDAWG85

600 cfm. Brand new fuel pump, Holley blue electric fuel pump, loud but pumps good. I put a vacuum gauge on in my garage and I've got good but not great vacuum. I have adjusted the carb as much as I can, it has white plastic "stoppers" on the lean screws so it will only go so far. But I have not checked vacuum while driving, I will. I can't imagine it would vapor lock, if anything I have moved the fuel lines away from heat more than it was originally. The stock metal fuel line that runs from back to front of truck is maybe 6 inches from exhaust manifold but that's how it came from factory so you would think it would be ok.

Braggs

Maybe there's an inline fuel filter that's clogged enough that it works in the driveway but not allowing enough through going down the road? There's also another filter built into the fuel inlet on the carb to check (even though you said it was a new carb).

Half ton

You may have a vacuum leak, check all the vacuum lines back to the rubber vacuum manifolds at the rear of the intake manifold.

Daniel k

I had a 76 merc that would do that same thing , I would be waiting to make a left turn in the middle of the intersection and it would just turn off !! , only happened when the car was at running temp . I would be out there cranking it over to no avail , then have to push the car out of the intersection , wait for about 20 minutes and it would start right up . I pinned it down to no spark , this car had the electronic ignition box on top of the fender well , aluminum looking box thing about 5 x 5 x 2 inch's and a module under the distributor cap that delivered the spark , I went to the junk yard and bought the box thing for $ 120 bucks , two days latter , there I was in the middle of the intersection cranking it over to no avail and pushing it to the side of the road . It turned out to be the little module under the distributer cap ( about 30 bucks ) the car had about 80 thousand miles on it ,

Half ton

Just sounds like either or the carb or a vacuum leak. Please let us know what the end result was ?.

hamviper

Just went through something similar on my 78, replaced all my soft fuel lines (at least the ones I could reach) and that solved my problem. Fuel lines were in rough shape, I can only guess that as the revs came up I was drawing air into the system. I have also heard of a fuel line degrading and the liner blocking the fuel pump inlet causing a similar problem. If anything it is cheap and easy to do. Might give it a try and see if it helps. Good luck.