Technical DELETE

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Maybe the gauge is not working right. Cold shows right reading?

 

I thought that too…but the way I initially found out was that I was driving the car and it died on me like it was starved of fuel.

checked that I had gas and then checked at the carbs and no they had no gas.

So the pressure is definitely dropping

 

Are you boiling the fuel (vapor lock)?

 

I've seen this before..
In a hi end build, They tried efi, Didn't have success, Went back to carb, But regulated the pump down to 4psi., The pump would eventually shut off, Let sit, fires up...
Changed the pump out to a 5psi.
Problem solved...
Higher psi pumps regulated down run very hot... Not knowing Your pump can't say, Just something to look into..

 

When did you last clean/replace the fuel filter?
Also, gauges can read low when things heat up.

 

This problem can/has also happened with liquid-filled fuel pressure gauges. Removing the liquid could solve the problem.

 

I have the same problem. When cold the gauge reads normal 5 LBS.
When hot, it goes negative, and takes a while to get started.
I have changed out the pump, filter, regulator etc., the problem
has been there for 10 years. I was wondering if the fuel in the carb is
boiling off when its hot.

 

Put a short clear line on the suction side of the pump. If the vacuume in the line is to great fuel can flash into bubbles and cause a pressure drop.

 

Think I figured it out! The problem has only started happening since I chromed the exhaust.

Part of the exhaust is really close to a fuel line so I will heat wrap it and see what happens!

The exhaust was painted Eastwood high heat paint before and was a whole lot cooler in temp!!

I'll keep y'all posted!!!

 

Is there any chance that your fuel line runs any where at or above the high point of the fuel level in the tank? Is your fuel pump located near the engine or nearer to the fuel tank?

 

I had this issue, the fuel pump was starting to fail, would be fine at start up and taper off while driving. Let it rest a bit and it would work again until it didn’t. It was one of those Napa pulse pumps, it would make noise but no fuel movement. Switched to a Carter pump and it’s been fine since.

 

Heat is the enemy of today's gasoline. Anything you can do to keep your fuel lines away from heat is a plus. Additionally, insulating the fuel line is also helpful. Hose is a better insulator than tubing. You get the idea.

Today's gasoline "boils" at ridiculously low temperatures. Fuel pumps can't pump vapor or bubbles. Always put an insulator between your carb and manifold and keep the fuel lines as far away from heat as possible.