#21  
Old 05-05-2020, 09:44 PM
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There is no bypass fitting and 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.

I don't know why the pump functioning has changed - especially with the return style regulator diaphragm changed - 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?
Thanks Again, Craig

  #22  
Old 05-06-2020, 11:12 AM
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Magnafuel makes good stuff.

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  #23  
Old 05-08-2020, 09:40 PM
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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

  #24  
Old 05-09-2020, 01:36 AM
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I had my money on the return line causing problems, but your last test ruled that out. Might be interesting to get a gauge on the supply side of the regulator to see if you are actually getting a big spike in pressure when first turned on that the regulator can't handle. If those pressures look decent, then I'm with the guys suggesting something momentarily sticking in the regulator.

Also surprised you only have a half pound residual pressure. I'm running 10-AN hose for a return and residual is a little over 2-1/2 pounds with the Mallory 250 pump.

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  #25  
Old 05-09-2020, 09:23 AM
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Anyone close you can borrow a bump to test?

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Old 05-09-2020, 10:21 AM
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You could try temporarily hooking up the pumps built in bypass, and disabling the bypass on the regulator to be able to narrow down the area of trouble. Similar to the test you did earlier, but it won't blow the fuse with the pumps bypass working correctly. I've only used the mallory 250 once, years ago, and it was plumbed with the pump bypass operative, and worked well.

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  #27  
Old 05-15-2020, 12:59 PM
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[QUOTE=lust4speed;6139418]I had my money on the return line causing problems, but your last test ruled that out. Might be interesting to get a gauge on the supply side of the regulator to see if you are actually getting a big spike in pressure when first turned on that the regulator can't handle. If those pressures look decent, then I'm with the guys suggesting something momentarily sticking in the regulator.

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

  #28  
Old 05-24-2020, 09:01 PM
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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

  #29  
Old 05-24-2020, 09:07 PM
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How did you do this latest test?

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  #30  
Old 05-24-2020, 09:39 PM
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Teed into supply line just before enters regulator.

  #31  
Old 05-27-2020, 11:10 AM
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If you were in Houston you could borrow my back up 250. . Just tested my return system this weekend regulator backed all the way out -2.5psi. Free flow line into a 5/8" line in a gas can 1.5psi.

You know the Mallory 110 puts out normal carb pressure yet their identical EFI pump puts out 40psi. There must be an internal regulator spring that is maybe stuck or trash in it. They sell a new gasket kit for them I used to refreshen one, might call Mallory tech

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  #32  
Old 05-28-2020, 09:06 AM
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Call Mallory and ask to talk to an Engineer/Tech. From my past experiences there are many variables that need to be considered. Alternatively you will just throw parts at it and never understand the underlying cause.

  #33  
Old 05-29-2020, 11:12 AM
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Never had any problems with my pump if you scrap it I will take it for parts .

  #34  
Old 06-01-2020, 09:07 PM
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Thanks guys for all the input.
After changing diaphragms in the regulator on the bottom of the pump and the regulator by the carburetor and playing with springs and testing all that I can – nothing seemed to change.
However, once the ambient temperature changed from the 60s to the 80s, the fuel pump would spike to 11 and then settled to six more quickly as to avoid bending the float tabs and flooding the motor.
Several years ago, Mallory tech was very hard to access and Mallory was then bought out by MSD to which now has been bought out by Holley and there is no tech support for this pump – you can just buy a new one if you want.

Decision: is to run it and see what happens.

Thanks for all you guys help – take good care, Craig

  #35  
Old 06-02-2020, 12:43 PM
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RobbMc used to work for Mallory. Might drop him a line and get his input.

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1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs
  #36  
Old 06-02-2020, 02:21 PM
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Thanks - Skip Fix - good idea!
I hate not being able to understand what is wrong and how to fix it.
Take Care, Craig

  #37  
Old 11-17-2020, 10:02 PM
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Thanks guys, just wanted to get back to you and let you know the issue was resolved by something very simple and that was the regulator had a vacuum signal port that had been blocked with a vacuum cover – as I thought it was for many years. Once removed to allow the diaphragm to move freely enough to resolve the issue. For everyone who indicated it was simply a regulator issue – You were absolutely right.
I also want to thank Skip Fix and RobbMc Performance products for taking the time to help me sort out the issue and also sell me a backup Regulator that works very well for a very reasonable price.
Thanks again everybody, Craig

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