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Discussion Starter #21
Thanks guys and juiced coupe 78 for your perseverance and trying to help me figure this out. The pumps return line has been capped since the beginning.
I have tried different ways of testing the regulation of the pump itself before the return regulator which should be between 15 and 20 psi per instructions. I've ordered extra fittings to block off the pressure to the carburetor and install a higher pressure gauge to monitor fuel pressure before the return regulator – the best way I can and that will be to turn the return regulator as high as it goes with a higher pressure gauge. I did try to deadhead the pressure before went into the regulator and it immediately spike to 100 psi and blew the fuse in the pump – obviously that didn't work.
Stay tuned as I will post the test results as soon as I get them.
Thanks again, Craig
 

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That 15-20# is when using the pump's bypass, and using deadhead regulators. With a return system, the pump's outlet pressure should only be slightly higher than the pressure at the regulator (and that is only because of restrictions).

With a return regulator, the pressure at the inlet and outlets is the same. Look inside your regulator, its a common chamber. The regulator acts as a pressure relief, bypassing some fuel back to the tank. This is why I said that if you can't lower the pressure, it is either a problem with the regulator not bypassing enough fuel (sticking?) or a restriction somewhere in the return line.
 

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Discussion Starter #23
That bypass external port was plugged from the beginning. I had thought that the damper diaphragm on the bottom of the pump was also for internal bypassing fuel like an oil pump. I guess it is more for the original external bypass for fuel to be regulated back to the cell - like you said - Thanks.

The issue of spiking to 10 - 11(+) PSI and then slowly (1 to 2 seconds) dropping to the 6 PSI. I don't know why the pump functioning has changed - especially with the return style regulator diaphragm changed (no improvement) - although I could not find the exact replacement anywhere and ordered one from holley and one from summit both a slightly different style even though the website shows the correct pictured item.

What return style regulator would you recommend for this pump? Mine is the 5-port Mallory 4300.
Thanks Again, Craig
 

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Before you get another regulator, verify that your return line isn't the problem. Run a section of hose from the return port into a fuel jug, and see if the problem still exists.

I've had the inner lining of hoses separate and restrict flow, particularly where the hose ends attach.
 

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Discussion Starter #25
when I run the pump with the regulator open as to 0 pressure to the carb I see a pressure of 1/2 PSI or less is that normal?
 

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Discussion Starter #28
Yes - totally open on the return line and O Pressure at the bowls.
I will find a way to test with the return line attached to fuel jug - per your suggestion. I just don't have any extra # 10 line and fittings. Perhaps need to go to #12 from regulator to cell?
From the beginng - to setup needed to go from #8 return to #10 just to get the pressure to lower to 6. Spent time with Mallory when they had a tech person.
 

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Discussion Starter #29
Thanks - this makes sense:

"I've had the inner lining of hoses separate and restrict flow, particularly where the hose ends attach."
 

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Discussion Starter #30
Latest test attached to the regulator return port with "3/4 ID tubing at '4 long into fuel jug - flashes to 11 1/2 PSI and settles to 6 PSI in 1 second or so. Immediately re-attached return line to the cell and got the same results. I even loosened the external adjust on the bottom of the pump with No Change.

The Pump? Does the pump have an internal pressure regulation even when the external bypass is blocked? The Regulator - even though I replaced the regulator diaphragm?
Thanks Again, Craig
 

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Discussion Starter #31
Hi guys, I have ordered more parts to use with a different gauge so that I can test this last supply-side pressure to see if there is a spike as a rule out and then looking to borrowing a pump or regulator to which I don't really have a resource.
I will let you know the results.
Thanks again, Craig
 

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Discussion Starter #32
Hi guys - Results on supply side test = the same spike to 11 PSI settles to 6.
Any ideas are welcome.
Take Good Care Everyone.
Craig
 

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Discussion Starter #37
Vent on tank is good and pump is at full bypass with regulator - thanks, Craig
 

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Not reading this again. If your running a bypass regulator block the bipass in the pump don’t need it maybe they are reacting to each other not everything you buy works the way it should.
 

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Discussion Starter #39
I run the Mallory Full Bypass regulator 4300 and have the bypass on the pump blocked - I wonder why the pump starts up and spikes to 11 PSI and then settles to 6 PSI in 1-2 seconds? 1/2 PSI residual return line pressure.
Normally don't pumps start and go to the set pressure immediately?
Yes - this is a little maddening.
Thanks, Craig
 

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If it settles within a couple seconds, I wouldn't think much of it.

The regulator is obviously closed when the pump is started and it takes a second for the system to balance.
 
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