#21  
Old 01-10-2023, 05:26 AM
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Cliff R Cliff R is offline
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My set-up used a Comp 140 gph pump with a 14psi spring. I ran a regulator before the carb to adjust pressure and it had a return back to the tank so wasn't "dead-head".

As part of the original testing I did when writing my book I removed the airhorn from the carbs and held the hinge pin down while adjusting pressure and watching the fuel level in the bowl.

Only the "early" Q-jets with the large float and short hinge pin were sensitive to high fuel pressure. The later varieties could EASILY take 10-12 psi without any flooding during a "static" test. I also did street and track testing and both later variety Q-jets were fine to at least 10 psi with a .135" N/S assembly installed.

I would add here that fuel pressure (as Kenth mention early in this thread) does effect fuel level with any particular float and fuel inlet seat diameter so plan accordingly.........

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  #22  
Old 01-10-2023, 11:28 AM
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Thanks for explaining how you measured the inlet capability. That is more direct than waiting for an assembled carb to overflow.

Sorry if this is old news to all of you but I found this interview with Carter interesting Link to Carter Interview. It appears to be a 2011 Rocky Rotella article.

What I liked the most were the attached cross-sections of the pumps. It's easy to see why a 3-line pump doesn't "recirculate" much fuel. I can finally see how the "vapor diverter" that feeds the return line (air vent to mitigate vapor lock) necks down to the small orifice others have described. When these pumps are "deadheading" against a closed seat, I don't see much fuel running through the return but I guess it's a "controlled leak" that could have some effect on max pressure if it was blocked.
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  #23  
Old 01-18-2023, 03:36 PM
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I've decided to replace my stock mechanical fuel pump (3-line short can).

north recommended Spectra Premium on another thread but I find they are no longer available. Spectra customer support told me they sold their pump line in 2020 and no longer sell their PN SP1161MP in the US. Autozone still markets Spectra pumps but they are a different PN so may be from the new owner of the Spectra line.

Does anyone have RECENT experience with Carter and/or Borg Warner/Delphi? Both have OE replacement pumps.

Carter M4885 says min pressure 5 psi, max 6.5 psi
Delphi MF0155 says "system pressure" 5 psi, max pressure 7 psi

I know my carb should be fine with 7 psi and I suspect it will be, just want to know if anyone has recent experience with either of these?

Thanks

Mike

  #24  
Old 01-18-2023, 04:45 PM
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It's hit and miss. Sometimes you get a good one, sometimes you don't.

No real quality difference between the stock OEM style pumps, whether it's Carter, AC, Spectrum, Delphi, or any of the other OEM stuff, take your pick.

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  #25  
Old 01-18-2023, 09:51 PM
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Thanks for the reply. I was hoping for better odds but after hearing Spectra had sold theirs off, it seems none of the suppliers feel quality is a big differentiator on these low-priced OE replacements.

The one on my car may be fine, but after replacing the tank and sender to lose a rust source, I figure it's easier to replace it than wonder about it.

I ordered a Delphi pump just because.. fingers crossed.

  #26  
Old 01-25-2023, 05:11 PM
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Quote:
Originally Posted by Cliff R View Post
....
As part of the original testing I did when writing my book I removed the airhorn from the carbs and held the hinge pin down while adjusting pressure and watching the fuel level in the bowl.

Only the "early" Q-jets with the large float and short hinge pin were sensitive to high fuel pressure. The later varieties could EASILY take 10-12 psi without any flooding during a "static" test. I also did street and track testing and both later variety Q-jets were fine to at least 10 psi with a .135" N/S assembly installed.
...
I finally got this done today. Filled bowl and tubing with gas, pressurized with a low-pressure regulator.

0.128" ID seat with the plastic float held great until 12 psi where it was overwhelmed.

So I will leave it alone, consider the inlet good, and move on to other stuff that may be messed up. It's certainly possible the pump was putting out more than 12 psi, but unlikely. Regardless, I have a new pump and my fingers are crossed.
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