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I have a local carburetor shop that does a great job on them. Myself, I am more miss than hit at rebuilding them. The time it takes me to get one back together and sorted, I can make the $$ to have the shop do it. Carry the unit in, get it back and bring the car back so they can tune it. Everyone wins.
 

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If the top of the carb is wet more than likely the needle & seat is leaking , either from dirt , damage , mal adjustment , bad float , something ! The top of the carb should be dry ! I don't know where you're located , but you need to find a scrap yard that doesn't crush everything older than 2010 ...other than the internal choke lever & link , qjets aren't any more difficult than any other carb IMO...
 

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'23 T-Bucket Pickup
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i'm thinking of just getting a holley 4175, not because i don't like quadrajets, but because i don't have time to dork around with a q-jet.

Anyways, what recently happened, after running ok is now i have no idle and i'm getting flooding.

The only thing i did was to adjust the secondary throttle plates to open more (the plates, NOT the air flap doors) and then did some "spirited testing" let's just say.... The jeg's reman q-jet shipped with the secondary plates really not opening at all. i got them to open about 30-40 degrees which is enough for now. i did this Monday night.

So, Tuesday morning, immediately after doing an acceleration test, i immediately noticed that the low speed and idle wasn't normal/as smooth as before. After work, i did another "test." After highway cruising about 15-20 mins came to a stoplight. Engine was really idling rough at this point. Then, at this stoplight, did another "test." After this is when the stalling/no idle/flooding happened at the next stoplight. This was Tuesday and before this everything ran fine.

-----timing very advanced but don't think this is the problem.

---- Choke works fine

---- fuel pressure last time i checked was about 5.5 lbs at idle. As soon as i open throttle it goes down to about 2.5-3.5.

---- "Normal" WAS 1000rpm neutral, 600rpm in gear. Won't do any of that anymore. If i put it in neutral and keep my foot on it i can get it to idle 800+rpm all day, as soon as i let up it putters out.

So to Sum: Engine will no longer idle and getting flooding. Ran good until immediately after adjusting the secondary throttle plates to open more and after doing acceleration tests.
Another problem that I have run into is the power valve piston sticking in the up position. This can happen for various reasons, most often gumming up of the power valve piston or bore, sometimes caused by carbon buildup, but can also be caused by the carb being on the shelf for an extended period of time. Wide open throttle drops engine vacuum and the spring under the power piston pushes the piston all the way up raising the metering rods which allows more fuel to flow into the primary venturies, which would produce the exact problem that you are experiencing. You have to pull the top of the carburetor off of the carburetor to access the power valve piston. I’ve only had this happen a few times, but it does happen. As I said, the symptoms of a power valve piston stuck in the up position ARE EXACTLY what you are experiencing. It’s an easy fix for someone experienced with Quadrajet carbs. Let us know.
 

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I don’t need to pull the carb lid off to check power piston movement.
I just use a small screwdriver and check for movement thru the vent tube.
Small pencil works too.
 

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I don’t need to pull the carb lid off to check power piston movement.
I just use a small screwdriver and check for movement thru the vent tube.
Small pencil works too.
That’s great. I wasn’t sure if your carburetor had that access. Keep in mind that it has been almost 11 years since I last worked on a Quadrajet carburetor. With the engine not running you should be able to push the piston down and the spring will push the piston back up, if it isn’t stuck.
 

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Also there is, of course, a small vacuum passage to pull the piston down. Remotely possible for it to be plugged. I’m sure that you know that the piston should be all the way down at idle. I’m sorry if I come across as if I question your knowledge of a Quadrajet. I’m just wanting to share what I know from experience. Never met a Quadrajet I couldn’t fix if I had it in my hands.
 

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If it’s leaking out of the vents around gaskets and the throttle shaft then that is float bowl overflow from the fill valve not shutting the flow into the bowl off.

Possible causes :

  • Fuel pressure too high, 5 to 7 psi is plenty.
  • Float level set incorrectly.
  • Float is leaking (brass) or soaking (plastic) fuel making it heavy and will not shut the inlet valve.
  • The metal tang that hinges the float and controls the inlet needle valve is loose at its attachment to the float.
  • The shut off valve is leaking across its seat this can be the valve body or the needle.
  • The gasket/washer that goes under the valve body is missing or the sealing surface of the carb body, washer, or valve body is marred or dirty.

There are a lot of combinations of parts out there this carb being front line production over many GM car lines and several other companies used this carb on some models including American Motors, Chrysler and Ford. GM alone used about 7 different floats. Meeting production criteria is not the same as Holley or Edelbrock supplies to the hot rod community.

Bogie
 

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Discussion Starter · #28 ·
Also there is, of course, a small vacuum passage to pull the piston down. Remotely possible for it to be plugged. I’m sure that you know that the piston should be all the way down at idle. I’m sorry if I come across as if I question your knowledge of a Quadrajet. I’m just wanting to share what I know from experience. Never met a Quadrajet I couldn’t fix if I had it in my hands.
No, please DO question anything i do concerning carbs; i'm more of a suspension / chassis person who is fascinated by engines, but maybe not the most natural engine person. Whereas most hotrodders seem to be primarily "engine people" first and foremost.....?
 

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Discussion Starter · #31 ·
the plastic ring should press fit into the housing---stake it lightly if you have to.
gasket goes on top.
Uh oh.............

So, just to be clear, the white, plastic ring should be flush with the fuel baffle (usually black)?
 

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Are you able to determine fuel pressure ? past 5-7 pounds the pressure can push past the needle and seat.
when you use an electric pump you should incorporate a pressure regulator and a fuel pressure gauge to make sure you are not overflowing past the needle and seat.......... just my 2 cents
 

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Discussion Starter · #34 ·
Should look like this, except White
Ok. i took the horn off and the o ring worked itself below the gasket (i had installed it ABOVE the gasket---because that's how i found it the first time not thinking it was right, but not knowing better....) Perhaps the airhorn pushed it down when i re-installed it?

Anyways, the metering rods themselves seem to be working right, so i don't think that was the problem.

i think i'm going to order a rebuild kit and do a quick rebuild, then measure pressure---my gauge may not have been right; See this writeup----my gauge is liquid filled and i don't trust it---can't get it to zero out. Going to order a non-liquid filled gauge tonight---likely the AutoGage #2311.

i'd like to install a new needle/seat/float, and new gaskets and make sure the idle passages are not plugged although i don't see how they could get plugged in less than 24 hours... Then test for leaks and fuel pressure. If that STILL doesn't work then try another q-jet, preferrably from a good rebuilder such as Cliff Ruggles. If THAT still doesn't work (can't imagine it won't), then move to a 4175 because i think i'm eventually going to go holley anyways since i like them too.

i'll start taking pics. icloud wasn't letting me transfer pictures from phone to computer, but i fixed it.
 

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Discussion Starter · #35 ·
Are you able to determine fuel pressure ? past 5-7 pounds the pressure can push past the needle and seat.
when you use an electric pump you should incorporate a pressure regulator and a fuel pressure gauge to make sure you are not overflowing past the needle and seat.......... just my 2 cents
The more i think about it, i'm thinking pressure may be the problem----i don't see what else it could be. When i was using a mechanical pump, i don't recall any problems. It's only when i switched to electric then i've got runablilty problems.

As you may know, chevy stopped putting the fuel pump hole and fuel pump mounting holes in blocks after around 87----and i'm running an 87 block wherase previously an 86.
 

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Not totally sure about this block, but I did the same thing and just a heads up it may be externally balanced and some of your rough running may be an imbalance if and in the event you may have an externally balanced engine and not realized it
 

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Discussion Starter · #37 ·
Not totally sure about this block, but I did the same thing and just a heads up it may be externally balanced and some of your rough running may be an imbalance if and in the event you may have an externally balanced engine and not realized it
This 4.3 v-6 does NOT have a balance shaft and yes it does NOT idle smooth, but this is NOT the problem.....
 

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Discussion Starter · #38 ·
Your thoughts on:

Larger needle+seat being riskier towards flooding? Or does it not matter how big as long as the needle, seat and float are good and fuel pressure is correct?
 

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I know this is on a Holley which is what I use on my builds. On the needle and seat the size makes no difference on how well it will handle the pressure in my experience. The main thing that makes the difference is the fuel pressure going to the needle and seat. I have ran stock .097 size needle and seats and the more performance size .110 size needle and seats on many different Holley style carbs over the years and it made no difference on how they reacted to fuel pressure.

If I had to much pressure both would flood in no time flat or if they got junk in them. I never had problems before with electric or mechanical fuel pumps back in the older days but three years I had to finally go to a fuel pressure regulator because of the modern fuel boiling to quickly vs in previous years and also a lot of the mechanical fuel pumps on small block chevy's for some reason can end up with pushing out over 9 psi out of the box. Never had that problem in the early 2000's but since the later years past 2010 I have read a lot of folks getting new pumps that are supposed to run no more then about 6 psi but end up at the 6 to 9 psi mark and that will make a carb flood very quickly regardless of what size needle and seat you use.

I got a return style fuel pressure regulator to the fuel keeps moving and to help combat fuel boiling when the vehicle is turned off and I have mine set at 5.5 psi and it has worked like a charm for me. Its almost recommended to run a return style line nowadays because of the difference in fuel compared to how it was years back. Fuel injection has been the standard for so long that the fuel is no longer really good for carbs along with the added ethanol which only complicates things. Get a book on how to rebuild Qjet carbs that Cliff Ruggles made and you can learn a lot about those carbs and it has a lot of good tips in it and on rebuilding etc.
 
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