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Old 04-19-2016, 04:47 PM
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Default Carburetors and fuel pressure: Please read

Over the last few months I've had several customers contact me regarding flooding & poor idle issues with carbs I've built for them. (FWIW, I'm referencing mainly Carter AFB's and Rochester Quadrajets)

I have no explanation as to why, but today's mechanical fuel pumps tend to put out <span style="font-weight: bold"><span style="font-style: italic"><span style="text-decoration: underline">WAAAY</span></span></span> too much fuel pressure. In all of the above instances, once I finally got the customers to verify their fuel pressure they were <span style="font-weight: bold"><span style="text-decoration: underline">all</span></span> 10 PSI or more!

Holleys tend to work best with 5-7 PSI. Rochester Quadrajets will not tolerate much over 5 psi. Carter AFB's and AVS carbs run best around 5-6 PSI. Carter WCFB and Rochester 4GC carbs do <span style="font-weight: bold"><span style="text-decoration: underline">not</span></span> like anything over 5 PSI.

Anything over these figures can and likely will result in flooding and driveability issues. In many recent instances, it's taken quite a bit of prodding on my part to get the customers to actually verify their fuel pressure. Unfortunately you can not take for granted that today's fuel pumps are within spec., you really do need to verify as part of your basic tuning process.
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Old 04-19-2016, 05:27 PM
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Default Re: Carburetors and fuel pressure: Please read

Do you know of good suppliers for fuel pumps?

I need one for my 1969 W31, for street use (not show/trailer) my original will sit aside for now.

Ryan
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Old 04-19-2016, 06:20 PM
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Default Re: Carburetors and fuel pressure: Please read

Ryan;

I'm currently researching OEM pumps, but for now all I can advise is something along the lines of a Carter or Holley stock replacement pump. The new AC Delco units are the ones I'm really seeing with issues at the moment.
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Old 04-19-2016, 06:34 PM
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Default Re: Carburetors and fuel pressure: Please read

Even the &quot;no name&quot; pump I had on my recent build was way high, like 12 psi.

Swapped to a Carter and it is still to high at 7, but not flooding a Q-jet.
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Old 04-19-2016, 07:36 PM
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Default Re: Carburetors and fuel pressure: Please read

Eric -- I have used the Airtex brand pumps over the years with no issues ... have you any dealings good or bad with that brand? Thanks ... TAZ
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Old 04-19-2016, 09:01 PM
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Default Re: Carburetors and fuel pressure: Please read

Maybe there is a time line with these?
I have 3 Airtex here that register 6-8psi.
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Old 06-22-2016, 06:39 PM
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Default Re: Carburetors and fuel pressure: Please read

We just put an 40987 AC Delco on a 1969 Z-28 and it flooded the engine. Test pressure was 10 PSI. Way to high. You can't trust anything anymore. As Snap On tools motto says: &quot;Test, don't guess&quot;

Bill
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Old 06-22-2016, 08:50 PM
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Default Re: Carburetors and fuel pressure: Please read

Another good reason to install a regulator ... TAZ
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Old 06-22-2016, 09:45 PM
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Default Re: Carburetors and fuel pressure: Please read

Putting a sbc in my 49 Studebaker truck. I gave up on mechanical fuel pumps and decided to use one of the little 12v electrical pumps that put our 4 to 6 psi. Cheaper too. I have 3 vehicles that have them and as an added bonus, if you haven't run the car in a few weeks, you turn on the key and wait for the pump to quit pumping. That means it has replaced all the evaporated fuel in the carb, so you don't have to crank too long to start.
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Old 06-23-2016, 02:29 AM
Big Block Bill Big Block Bill is offline
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Default Re: Carburetors and fuel pressure: Please read

But how do you install a regulator and or an electric pump on an original paint 100 point, Benchmark, 14,000 mile Azure Blue 1969 Z-28 and get away with it? Doesn't anyone make a repop correct looking and WORKING fuel pump any more? You would think someone would see a need for such a part and reproduce it.

Bill
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