I just bought a '63 LeSabre with the stock 401, 82k miles. I have fluctuating fuel pressure. When the fuel pressure is up the motor runs perfect. Sometimes the fuel pressure will drop and the filter empties out and it runs rough and dies. It is a clear filter so I can see it is getting some fuel, but not enough. I have pulled the tank and had it cleaned, replaced all fuel lines, replaced fuel pump, tore down the carb and went through all vaccuum passages and jets, and it still doesn't have consitent fuel pressure. I am stumped at this point. Any ideas?
Just a long shot. Check and see if the gas line is touching any hot surfaces. Could be a vapor lock situation.
Have you checked it with a fuel pressure gauge, or are you just going by what you see in the clear filter? Depending on the orientation of the filter, there may always be some air in it, giving you the impression that it is not getting enough fuel. And in order for the filter to "empty out" as you described, it would need to be higher than the carburetor, because a carburetor will not create a vacuum and draw fuel out of a filter.
I haven't checked it with a guage. The filter is below the carb. When it is full, the car runs great. When it is empty, car runs poorly-starved of fuel. What would cause the filter to empty?
If the filter is getting air in it, it is most likely getting in somewhere on the suction side of the fuel pump. If it was on the pressure side, you would have fuel spraying out wherever the leak is. I had a friend with an O/T Chevelle that would die every time he went around a broad sweeping right hand turn. Turned out there was a hole worn through the fuel line which was normally covered up enough by whatever was rubbing on it to seal pretty good, but in those sweeping right handers there was enough body and frame flex to uncover the hole, the fuel pump would suck air, and the engine would die after the carb bowl level got low.
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