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I had a Holley blue electric fuel pump feeding the 4150 on my 454. It used the stock tank draw tube (3/8"?), and 1/2" lines from there to the the carb. between the tank and the pump is a big Fram cartridge filter. I hooked up a gauge right before I removed all this, and the pressure was 4.5 PSI with the electric.

I did some rework, starting at the tank, using the same stock line to draw from the tank. It goes to the filter in 1/2", and I replaced the cartridge while doing this other work. From there, I go 1/2" lines to a new Holley 12-454 mechanical pump. From there, I go 1/2" lines to a new Holley fuel log. I put on the same Holley pressure gauge (that I used to check the old system), one of those liquid filled units.

ANYWAY, when I start the car cold, I get 8 PSI at idle. When the car is fully warmed up, it drops to about 2 PSI! What is going on? It runs OK, but I haven't had time to give it a full throttle burst to see if it starves, and I haven't had anyone around to blip the throttle while I am looking under the hood at the guage to see if the pressure climbs proportionately with RPM.

Do Mechanical pumps drop pressure somewhat when they are hot? Are liquid filled guages flakey? What gives?

Thanks for any help.
 

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Ken,
I have seen the small liquid filled (and non-filled) gauges fluctuate greatly from time to time. I am not real impressed with them. No particular brand either. Get a large high quality gauge and check the pressure before you condemn the fuel system. You can use an oil pressure gauge, it really does not care what it is checking. Just my two cents worth, it seems like you did an awful lot of work, but still have the stock 3/8 pickup tube restricting flow. The mechanical pump should not lose pressure when hot. I do think that you will eventually have to replace the fuel pickup tube in order to see any improvement from the system. Hope this helps.

------------------
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
 

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Ken, Some time ago I had the same type problem. First I went for the pickup tube which has a sack type screen. It was clogged with varnish from all those years of sitting. Cleaned the tank and replaced the pickup. Then it happened again. I was running out of fuel at different RPM's. Turned out that the diaphragm in the mechanical pump was weak. Replaced the diaphragm and all was good.
Good luck
 
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