[68blkbrd]

I have a problem that mimicked vapor lock but now have pinpointed the problem to the carburetor. The fuel pump works fine and the pressure is great UNTIL the engine comes to temp (175). The fuel filter then looks near empty , fuel is just gurgling into the fuel filter and the car bogs upon accelleration. I removed the gas line coming from the carburetor including the filter (gas then came into the filter and sprayed out) and started the car; the pump is pumping plenty of gas(maybe an oz. or so a second). So... something in the carb is restricting gas flow. The carb is a newer Holley 750 vac sec. The floats are set correctly. What should I check first on the carb? We're talking obstruction or malfunction only when it comes up to temp. I always ran a fuel filter on this carb. Should I completely rebuild? Any tips would be greatly appreciated. Thanks!

[68blkbrd]

I have a problem that mimicked vapor lock but now have pinpointed the problem to the carburetor. The fuel pump works fine and the pressure is great UNTIL the engine comes to temp (175). The fuel filter then looks near empty , fuel is just gurgling into the fuel filter and the car bogs upon accelleration. I removed the gas line coming from the carburetor including the filter (gas then came into the filter and sprayed out) and started the car; the pump is pumping plenty of gas(maybe an oz. or so a second). So... something in the carb is restricting gas flow. The carb is a newer Holley 750 vac sec. The floats are set correctly. What should I check first on the carb? We're talking obstruction or malfunction only when it comes up to temp. I always ran a fuel filter on this carb. Should I completely rebuild? Any tips would be greatly appreciated. Thanks!

[bmpmdf]

Does your Holley have the screens behind the inlets?

[krisr]

Mechanical fuel pump?

I had issues with fuel pressure with my mechanical pump getting hot and pressure would be in the 1-2psi area and 3-4psi when revving.

I had figured it was the diaphragm heating up with the engine and expanding or something something internally i suppose.

Convert to electric pump and blockoff the hole in the timing cover and I got constant pressure all the time and the filter is constantly full of fuel.

Hope it helps, its just what I found.

[Ryche400]

I dont think its the carb. Sounds like the fuel pump. If the screen was plugged up, the filter would still be full. Make sure all the fuel lines are away from heat.

[Thumpin455_GTO]

If tis dyin off around the top of first or just after hitting 2nd, its the pump. It cant pull the fuel from the back well enough to overcome the acceleration of the car. Assuming its mechanical.

Install an electric near the tank as low as possible without ground clearnace issues, and do like krisr said, block off the mechanical pump. You will be happier, I run a Carter street pump, the 7 psi one. It has gotten me into the 11's so it will get you enough fuel, I dont have a regualtor on it either. Holley 850dp on 11.3:1 455.