Help! Holley 750 doesn’t draw any fuel

[1983calais]

Just as the title says, i have an AED Holley carb that doesn’t draw any fuel at idle or any where in the rpm range. I built a 388 for a guy and just fired it the other day with this AED mechanical second carb that I rebuilt. I have good fuel pressure, fu in the bowls are at the bottom of the sight glass, fuel shoots out of the squirters, but it won’t idle or run at any position of the throttle blades. It will only run if I keep pumping fuel out of the squirters. I pump it a couple times and hold the throttle open, it dies as soon as it burns all that fuel up. I can’t keep it running long enough to check for a vacuum leak. I tore the carb completely down about 4 more times cleaning everything with carb cleaner and compressed air and still have the same issue. Now this is a forged balanced rotating asssembly with a comp solid roller cam. I double checked the valve lash and all is good. I grabbed another 750 Holley double pumper that is another customers, bolted it on and the engine runs great at idle, off idle response is perfect, and upper rpm range is great. I have rebuilt many diff carbs and have never run into this before. Anyone have any ideas or suggestions? Much appreciated everyone!

 

[bracketchev1221]

What do the boosters look like.? It’s physics if the air is passing through the venturi in the booster and there’s fuel covering the jets in the bowl it has to pull it out. If there is a booster issue and it’s not creating the low pressure area or the passage wasn’t finish drilled to the main well then it won’t.

 

[UC645]

Take it apart and verify all your gaskets are correct, and not blocking any necessary passages. I had a QFT that acted similarly, it wouldn’t idle but it would run if you held the throttle open and let it pull fuel through the boosters.
Someone put it together with a Holley baseplate gasket and not a QFT one, blocking the idle discharge ports.

 

[1983calais]

I matched the gaskets up when I rebuilt it and checked all of them again. I also verified all the holes and passages matched with the gaskets. It has downleg boosters and if I blow air through the air bleed, it blows fuel out of the booster. This carb was on a running engine about 10 years ago. It was taken off and put on the shelf by a friend of mine. I’m sure I’m overlooking something but I can’t figure out what.

 

[CopperNick]

Idle mixture screws baselined at about a turn and a half from the bottom? Idle stop screw turned in just enough to barely lift the butterflies and reveal the idle bypass port?

Nick

 

[1983calais]

Idle mixture screws baselined at about a turn and a half from the bottom? Idle stop screw turned in just enough to barely lift the butterflies and reveal the idle bypass port?

Nick

Yes sir

 

[SoFloG]

Vacuum leak around carb base, is there a spacer, intake manifold leak?

 

[CopperNick]

Left field drive here, is the Carb base plate to manifold mounting surface flat? No burrs or nicks?? Carb body to butterfly plate hasn't squished or pushed out???


Gotta be some kind of one off weirdness that is the culprit here.


Nick

 

[1983calais]

Vacuum leak around carb base, is there a spacer, intake manifold leak?

No spacer and I even reused the carb gasket on the Holley carb that is on it now to rule that out. It runs perfect with this carb on it so I don’t think it has a vacuum leak

 

[1983calais]

Left field drive here, is the Carb base plate to manifold mounting surface flat? No burrs or nicks?? Carb body to butterfly plate hasn't squished or pushed out???


Gotta be some kind of one off weirdness that is the culprit here.


Nick

I agree. The base plate is flat and no nicks or scratches. The gasket between the body and baseplate is new and hasn’t squeezed out. I haven’t had time this week to mess with it anymore but I’m hoping to this weekend. I have plenty of other gaskets in my cabinet and parts so I’m going to start comparing and inspecting everything again this weekend I hope.