[CraigG.]

Hey Everybody,
My old reliable Mallory 250 pump and Mallory 4300 regulator has worked very well for years. Now had sat for 1+ years and When start the pump it flashes to 9+ PSI and bends the tabs on the floats for 2 seconds to settle down to 6 PSI. I have been using E85 for years and the pump and regulator are gas type and have worked well.

I replaced the regulator diaphragm (by the carb) with the same results. I wonder if the regulator diaphragm on the bottom of the pump has gotten hard and less responsive?

I am stumped.
Thanks, Craig

[Skip Fix]

They used to refurbish pumps for a reasonable fee.

[CraigG.]

Any thoughts about the 9 yr old spring on the carb regulator getting weak - spongy?

[Chief of the 60's]

I run 9 to 9-1/2 lbs. with no problem.

[CraigG.]

New needle assembly is for E85 and builder says 9+ too high = blow off seats.

[Fast 69]

Make sure the bypass plunger in the pump isnt sticking.

[ponjohn]

If the return line is plugged or flow is compromised ( broken down from E85?) it will effect the regulated pressure.

[CraigG.]

Q. When you start your pump and bump - will it go directly to the set PSI and not rise above it? It that normal?
Q. The exploded diagram does not show a plunger - only a diaphragm and springs?
Thanks, Craig

[CraigG.]

Return line seems clear.

[Fast 69]

Yours may be different from mine but theres is a nut and set screw on the side of the pump body. If you loosen the nut and remove the set screw, there is a spring and plunger that acts as an internal bypass. That plunger sometimes gets sticky. If you are using a return style regulator, you need to remove the spring and Mallory makes a solid spacer that replaces it so the plunger stays seated and all of the fuel goes to the regulator.

[charlie66]

Can you borrow another regulator . Try another regulator..

[CraigG.]

Thanks guys for all your help - I ordered the alcohol repair pump kit with the damper diaphragm to replace.

I will let you know the results.

Take Care, Craig

[CraigG.]

Hey Guys,
Update: I have replaced the regulator diaphragm for the carburetor and had no change in the spiking of fuel pressure.
I recently replaced the pump diaphragm and kept the original pressure adjustment spring and replaced the damper spring for the diaphragm which counteracts the pressure from the pressure adjusting spring.
It has improved to the point where it does not bend the float tabs – however it still spikes at least 3 psi above setpoint and then takes a second or so to come down to the six psi setting.
Question: Is it possible that the pump bypass is bouncing once initially started?
1. Therefore, would it be helpful to replace the original pressure adjusting spring as it seems softer than the new one?
2. Would it be helpful to stretch the damper spring slightly to help stabilize movement and counterbalance the diaphragm when the pump starts?
Thank you guys for all your help,
Craig

[Scott65]

Is the return line at least as big as the supply line?

[CraigG.]

Supply #8 return #10 - 1/2 a pound of backpressure on return line

[Scott65]

Originally Posted by Fast 69

If you are using a return style regulator, you need to remove the spring and Mallory makes a solid spacer that replaces it so the plunger stays seated and all of the fuel goes to the regulator.

^ Maybe investigate this further?

[mysticmissle]

can you check the bypass pressure, to see what the spring is doing??

[CraigG.]

yes I will again

[CraigG.]

Thanks guys 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

[Fast 69]

Your pump has a bypass fitting on it? By that I mean a fitting that takes fuel directly from the pump discharge back to the fuel cell? I've never seen a Mallory 250 or any pump that size have that? Its usually only on 400 or bigger pumps. If it does have that then I would cap that and send all the fuel to the regulator. I run a Magnafuel 500 with that same size supply and return lines without any issues.