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Carburetor Problem?

Posted By charliemccraney 7 Months Ago
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charliemccraney
Posted 7 Months Ago
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I've been having an intermittent issue with missfiring and one time an absolute lack of power.  Most of my ignition system was 10 years old and I did find some issues there and have corrected them.  Hoped that was it.  While checking timing after the install of the ignition stuff it would not idle well but it did eventually clear up.  The real short test drive went well and when I got to my driveway it was idling poorly again.

It seems to rev and hold higher rpm well well but won't idle well in the garage, no load.  It will stall unless I give it some throttle once in a while and is difficult to start if it does stall like it is flooding  So I pulled the aircleaner and looked down the venturis and found fuel coming from the passenger side primary booster, with the throttle closed, in the idle position.  Further, I turned the idle adjustment screws all the way in and it kept running.  So my thought is bad power valve or gasket or bad needle/seat assembly, or a sunken float.  I then unscrewed the sight plug and fuel poored out like a miniature fire hose for about half a second, seeming to support the bad float or needle idea.

Then I though "what about fuel pressure."  The pump is electric.  I checked that and 12psi is indicated on the gauge, the maximum of my regulator.  I tried another gauge and still 12psi so no issue with the gauge.  The problem there is that the fuel pump is rated for a 7-9psi but when I installed it, the most I could get was about 5psi so I'm confused about this 12psi indication. If I just let the pump run with the engine off, no fuel overflows anywhere,as if the needle seat, and float is working properly.

The carburetor is a Holley 570 Street Avenger, center hung float bowls.  I did remove the needle and seat assembly.  The o-ring looks grey and powder like on the outside, where it contacts the bore of the needle/seat cavity of the float bowl.  It looks like it may be cracked part of the way around the perimeter but it could also be a molding line from the original manufacturing of the o-ring as I don't know what these should look like when brand new.  The needle itself looks ok.  I don't really know what to look for but it looks good to me.  I can see where it contacts the seat but I don't think it looks significantly worn or anything like that.  The carburetor is about 10 years old at this point about July of 2009 that it was installed.

I didn't dig any deeper because I don't understand how there can be 12psi of pressure if the pump is not capable of that.  That must mean something.
Maybe if the pump was dead headed it could peak higher than it's rating?  But, particularly, if the engine is getting flooded at idle, and seems to rev and hold higher rpm, it wouldn't have that issue, right?

It seems like it may no longer be intermittent.  Hopefully it stays that way so I can get to the bottom of it.




Lawrenceville, GA
57RancheroJim
Posted 7 Months Ago
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I don't use electric fuel pumps but I assume they have some type of pressure controlling relief valve and it may have been destroyed by the Ethonal fuel. Same with any other rubber carburetor parts. Over the last few years I have been having to replace, pumps, carb parts, fuel lines etc in all my old cars.
Ted
Posted 7 Months Ago
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I agree that there is some kind of regulator or bypass valve in the electric fuel pump that is not functioning correctly.  I’ll suggest looking at the fuel pump first.


Lorena, Texas (South of Waco)


charliemccraney
Posted 7 Months Ago
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I did get a reply this morning from Carter that it is possible for this to happen if the internal regulator is stuck closed or mostly closed.
The question then becomes why isn't my Aeromotive regulator controlling the pressure to the carburetor.  Hope to hear from them today.  Maybe beyond some point, it can no longer control it.  Something I forgot to mention originally is that the pressure will not change with any change in the position of the regulator adjustment screw - it stays at 12psi no matter what.


Lawrenceville, GA
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I pulled the plunger assy. from a used pump and here is what it looks like. There is a regulating system within the pump. I might add that the plunger needed to be coaxed with a strong magnet to get it to come out. Looks like a neoprene surface opposite the spring end so being exposed to our alcohol fuel may have a negative effect on these also.  This is a Holley branded pump but chances are, others may have a similar system.  It is, however, non adjustable, or,  at least not intended to be.  Good luck, JEFF..................http://forums.y-blocksforever.com/uploads/images/d32bddc9-8861-46cb-9fb0-246e.jpg


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Joe D
Posted 7 Months Ago
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Charlie,
Make sure the gage is ok. Depressurize line to ensure gage goes to zero.
Hope this helps.
Good luck.




Joe D (The Frig)
1960 F-100 - 292 Y-Block
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Do you have a separate pressure regulator in the line,  or are you relying on the pump alone?   I don't think the carb problem is related,  your not overflowing at the bowl.   The only thing that might mess with that is if the regulator starts working or allows the pressure to drop all of a sudden and you lose flow to the carb . 
The white powder in the carb is from the alcohol eating into the zinc of the carb.   I'd suggest a rebuild.   I went through that issue about 5 years ago.   I got a big load of alcohol in my gas.  It ate into the bowl a little and I had quite a bit of that white powder  in the bottom of the bowl.  It actually plugged up my idle circuits and was eating up the rubber in the accelerator pump.  I did a rebuild and it fixed everything.   2 barrel Holley


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paul2748
Posted 7 Months Ago
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What does the carb say for max pressure? If less than 12 it may be too much pressure for the needle and seat.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

miker
Posted 7 Months Ago
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Charlie, I’ve owned several Aeromotive pressure regulators. Boost referenced, EFI, they all just work. If yours doesn’t pull it apart and look for contamination. This doesn’t address the pump problem, but I’ve gone from 5lbs and boost reference to 40 lbs for EFI by just changing the springs in them. If its passing more pressure, it’s got to have junk holding it open. IIRC they are all alcohol rated, and the springs come in pressure ratings so look for something upstream from it. Or a spring the pump is pushing past.

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charliemccraney
Posted 7 Months Ago
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I replaced the pump with my lower pressure spare and the pressure is now under control.  I reinstalled the float needle / seat and am able to adjust the float level and it doesn't seem to be flooding because of pressure or float / needle related issues anymore.  The problem still exists, no matter the float level so I will dig deeper.

Is there an easy way to test a power valve or is it just easiest to replace it and see what  happens?

The Carter does not seem to have an externally accessible regulator.  Maybe I'll take it apart to see how it works.  I couldn't get the Holleys to last.  It is a much different design, and made in the USA, at least 7 years ago, they were.

When I said powder, I was only using that to try to describe the texture of the o-ring.  I did not notice anything that was actually powder or grit.  I've had the bowls off a couple times over the years probably 2-3 years most recently.  It's always been clean.  Who knows, maybe something has changed since then.  I'll find out soon.


Lawrenceville, GA


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