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Discussion Starter · #1 ·
I'm running a mechanical fuel pump with a pressure regulator on a dual feed 750 cfm Holley.
This a blower car (B&M 144) sitting atop a 355 cid sbc.
Problem...my fuel pressure is all over the place. Anywhere from 6.5 to 3 psi.
After the car sits overnight and upon start-up the gauge reads approx. 6.5 psi although after it warms up the pressure drops to the 3 psi.
Also, the regulator doesn't respond to any adjustment up or down.
Is this caused by a faulty pump, regulator or both?
 

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is there a return from the regulator?if not no other place for fuel to go except carb and i think you notice that.sounds like pump problem
 

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Discussion Starter · #3 ·
No, there is no fuel return. So, you think this inconsistent fuel pressure is due to a faulty pump. Alright, well help me here...if the mechanical pump is bad would that not be an indication of a failed diaphragm? Or does a mechanical pumps output just diminished over time?
 

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I went through the same problem, changed everything, finally decided to get a new tank with the pump built into it called tanks Inc and talked to them about what was going on. He said that if I had a Liquid filled gauge that the pressure in the gauge would drop 4 psi when it gets hot. Well I ordered the tank any way been wanting one and bought a cheap none fill Gauge to replace the one at the carb and now it reads correctly and will not change after getting hot.

I think I may have solved my problem I hope it may help you as well !!!
 

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Discussion Starter · #12 ·
Glycerin filled gauges are designed to limit shock to the internal bourdon tube movement. Heat hasn't any effect. If anything a cheaper gauge will do one of two things...discolor or leak depending on the construction.
 

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Well all i can tell ya is what the man at Tanks INC said,I have a 177 B&M blower under the hood and they do get a little warmer under the hood than just a regular engine. It worked for me.

Now grant it there are a lot of other things that can couse the same symtoms
and i went though all of them just to find out it was just the gauge and i tryed other filled gauges thinking it was bad gauges put a none filled one on there and problem gone.
 

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what happens is the glycering heats up inside the gauge raising the gauge housings internal pressure. this in turn drives the boron tube the opposite direction inside the gauge sending the needle back towards zero. venting the gauge housing and draining the fluid eliminates this.
 

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It's wise to run a return line.

If the "In" "Out" lines on the regulator are switched or regulators with a "Return" line are plumbed wrong you can have that problem. I somehow got the line feeding the carb coming from the return and my fuel pressure was 3 lbs sometimes and 12 lbs other times. No pattern when the readings would register high and low. Adjusting pressure made no difference. Although the engine ran good when it was like that, I needed to fix it. I finally found the problem. Switched the lines and it has been steady since.
But it is a good idea to run a return.

Don
 

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Discussion Starter · #17 ·
Never heard of the glycerine driving the needle in the opposite direction. Stranger things have happened.
NOT going to rule out a bad guage and will install a replacement before wrenching on the fuel pump.
Fuel lines are routed correctly.
 

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the same thing can happen in a dry gauge if the housing is sealed . heated air is a powerful thing.
 

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all i did was drain the glycerin, then, put the PLUG BACK IN. i`ll pull the plug. however, the fuel pressure DID drop, for i opened her up a little and it was stumbling.
 
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