Frustrating scenario. Truck runs and drives all day under 50mph. But try and go much over that and the engine acts like it looses fuel or spark completely. Starts surging and will not respond to throttle input.

If I pop it in Nuetral it free revs really well. Pop it back in gear and it bogs again.

New carb
GM HEI
New fuel lines
Clean gas tank
New fuel pump.

All parts have less than 500 miles on them.

It's a 289 with a c4

Have you done a re-curve on the distributor? sounds like the problem my son is having, frunniong out of advance.

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It does not matter what you think, it only matters what you do about it!

I have not. I will do a little research never heard of that!

I don't know what gearing you are running, but HEI and clones are notorious for spark issues above 4400. Test, test, test! Check the carb inlet screen if so equipped, check fuel pressure and volume, check coil, and above all, check all grounds! Look carefully at inside of distributor cap for carbon tracking, another HEI weakness. If distributor mounted coil, heat can cause a coil failure, especially on the Chines clones.
Paul

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The Ford Orphanage
Life's too short for boring vehicles!
My quest to develop a universal solvent is held up by the lack of a storage container.
Paul

Check your gas cap first. Is it vented? If so is the vent plugged? Loosen it and go drive it. If the problem still exists it is not the cap. You say the carb is new. Did you check your jets? Sounds like a fuel issue to me. Pull the jets and go 2 or 3 sizes bigger. If the problem goes away, great. If it gets better but still does it a little bit go up 1 more size and drive it. I think you have a bad lean issue.

Looks like your issue is maintaining under a load.. Likely fuel or spark as others mentioned. Do you happen to have a high micron fuel filter before the fuel pump? A broken down ignition wire not maintaining the coil? Try a known good ignition and retest.

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Chris

My bet.... Weak fuel pump or sucking air on gasoline inlet

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[b]'' I think what scares me the most about you guys is that I understand you '' ..... KID
'' lookin good, a little paint adds at least 100hp!'' ....... COOTER
'' well an old guy can dream cant he? ''............ICEMAN
''I would donate organs before selling my slick''........ HOOFBEAT RACER

Interesting idea. I have noticed some air in the glass filter. Not sure if that is normal for mechanical pumps. The pump has less than 500 miles on it spin hope it's not the pump.

I can put my old pump back in and test that theory.

I will check the fitting at the tank

There will always be air in the filter. It is not your pump. What carb do you have on it. You stated you have a new carb. Carbs are not one size fits all install and run. they take tuning I have never put a carb on anything that did not need some sort of tuning. You have a lean condition at load/speed. When you pop it in neutral and rev it with no issues you are removing the load, hence it revs fine. Check your jetting or power valve. If it is a Holley your power valve if wrong could cause those problems also. You will need a vacumn gauge to see what power valve you need.

Simple things can cause fuel problems. First check for collapsing fuel lines. There are two rubber lines installed in your fuel line. One is under the cab and one is under the hood. First thing I would check. If old I would replace anyway. Doesn't cost but the price of a piece of hose. Carb float could also be an issue, as if set to low and not getting enough fuel.

Rich

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1961 F350
1964 Galaxie convertable
1964 flairside, style side, and longbed
1965 Ranger, and shortbed
1966 long bed, and shortbed
A few parts trucks also
1991 Capri
2011 F250
2004 Lexus

The truck was running really well with my current setup and then out of the blue started this.

The carb is a new in the box edelbrock. It ran amazing. I did some minor off idle adjustments but other than that it hasn't been adjusted.

I did replace all the sections of rubber lines (under the cab too)

I picked up a coil this morning (they are cheap) so I will check all settings and change the coil and see what is going on. I do feel like it is spark related because the truck out of load will rev all day. I am really appreciative of your ideas. I will try everything listed!

Well got under the hood today to swap the coil and found a massive fuel leak at the carb inlet. Not sure what happened there but it was spraying everywhere. Can't believe I never smelled the fuel. Here is to hoping that was the problem so I can go back to feeling comfortable driving this beast around. I will test drive it tomorrow!

Well I went for a long mixed drive in traffic, back roads, and interstate. I can with some confidence say that I believe the fuel leak was the source of my issue. The truck behaved well.

Thanks for the advice.

Just kidding it did it again today... It's definetly fuel. Grrr

The three bends in the steel line, particularly the one under the cab will trap rust and cause fuel to bottle neck. Did you loosen the fuel cap as skidoorulzs suggested? I had no problems from my all stock 352 2 barrel. I put my built up 390 in it and found 4 fuel restrictions. Rust in the 5/16" steel line cab bend, flare restriction (line to tank) in the LMC gas tank, fuel pump, I upgraded to new 3/8" line and Carter fuel pump. Last no brainer was to move fuel filter after pump. I had installed it before to keep rust out of the pump.

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Chris

Remember the old " fill up a pop bottle test " for fuel pumps ?
It doesn't work......
I had a pump when discharging in an open container
Had a very good flow....
But it made zero pressure.....

I still betting on pump

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[b]'' I think what scares me the most about you guys is that I understand you '' ..... KID
'' lookin good, a little paint adds at least 100hp!'' ....... COOTER
'' well an old guy can dream cant he? ''............ICEMAN
''I would donate organs before selling my slick''........ HOOFBEAT RACER

I will swap pumps.

Here is how I got it home.. When it would choke and try to die, or successfully die I would put it in nuetral and let it idle for a few seconds and I assume the bowls would fill back up.

I after I did that the truck would drive fine again until I had to sit at a traffic light etc. I noticed that the truck would run warm (210+) when the issues would occur. I am starting to think that I am boiling the fuel in the bowls and vapor locking it...thoughts?

A lean condition will make a engine run warm. I throw my vote in for fuel pump also.

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Every day above ground is a good one

Does no one test anymore? My experience with simply replacing parts is that it tends to complicate things when the parts replacement doesn't solve the problem!
Paul

_________________
The Ford Orphanage
Life's too short for boring vehicles!
My quest to develop a universal solvent is held up by the lack of a storage container.
Paul

I often would rather replace parts and know they are "good". The stuff is so inexpensive my time seems more valuable than attempting to test a part. More money than brains? I would like to know "why" a failure occurs. Hence the post.