Quadrajet Accelerator pump issue
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
Quadrajet Accelerator pump issue
When I actuate the pump piston on the front left hand corner of my quadrajet I can see/hear no response. I am used to being able to see and hear a squirt of gas from the accelerator pump on other carbs.
Is the pump bad or is it difficult to detect the gas squirt on a QJ?
Is the pump bad or is it difficult to detect the gas squirt on a QJ?
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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If so the plugs could be leaking all the gas out of the carb, But before you tare the carb apart start the car and it run for 2 minutes then shut it off. Pull the air cleaner and look down the carb while you move the throttle linkage. If you now see two streams of fuel shooting into the primaries than the accelerator pump is working, if not than the accelerator pump may be bad and need to be replaced.
Another test: with the motor a operating temps and your at a light does the car BOG and then start to accelerate? That to could be caused by a bad accelerator pump.
Lars has some good posts on troubleshooting carb problems, but here is one with some pictures.
http://www.4wheelnoffroad.com/qjet.html
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
thanks for the advice, all
The car is very hard to start cold. I often use a squirt of starting fluid, and with just a quick spray it starts right up and runs great. I have heard about the leaking fuel bowl issue. I'll try the tip to run the car a few minutes (filling the bowls if they leaked), then try the accelerator pump again. I think it's the pump because I'm sure when I tested for a squirt last, the car had been run.
However, no real stumble on acceleration, which is hard to rectify with a bad accelerator pump. No question there is no squirt of gas though.
The car is very hard to start cold. I often use a squirt of starting fluid, and with just a quick spray it starts right up and runs great. I have heard about the leaking fuel bowl issue. I'll try the tip to run the car a few minutes (filling the bowls if they leaked), then try the accelerator pump again. I think it's the pump because I'm sure when I tested for a squirt last, the car had been run.
However, no real stumble on acceleration, which is hard to rectify with a bad accelerator pump. No question there is no squirt of gas though.
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Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
This certainly makes sense.
The carb was rebuilt a few years ago. P/O sent it to Woodruff carburetors in Ohio for the job. Would think an outfit like that would be well aware of the plug leak issue and fixed it with epoxy.
We'll see.
The carb was rebuilt a few years ago. P/O sent it to Woodruff carburetors in Ohio for the job. Would think an outfit like that would be well aware of the plug leak issue and fixed it with epoxy.
We'll see.
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
OK
so I spoke with Craig Woodruff at Woodruff Carburetors. He told me that the leaking well plug issue (causing empty fuel bowls) is actually very unusual on QJs despite the "conventional wisdom" that this is common. This actually agrees with Lars Grimrud according to his paper on QJ problems. Woodruff did say that the fuel bowl is commonly empty due to evaporation after a few days (the additives in newer fuels he says??).
So I took the top of the carb off today and removed the accel. pump. It looked perfect consistent with a recently rebuilt carb.
THE FUEL BOWL was EMPTY. So obviously thats part of the problem. ?evaporation or leak.
But, when I filled the bowl with gas, still no pump squirt. Weird. Looked at the accel pump again and put on a new seal. No squirt. Put it back together and drove it. No stumble on acceleration.
Bizzaro. I love workin' on old cars.
One other thing I noticed is that the air horn seemed warped which according to Lars is another common problem. It's not terrible, but maybe it could be related.
Fire away with your thoughts Gentlemen...
so I spoke with Craig Woodruff at Woodruff Carburetors. He told me that the leaking well plug issue (causing empty fuel bowls) is actually very unusual on QJs despite the "conventional wisdom" that this is common. This actually agrees with Lars Grimrud according to his paper on QJ problems. Woodruff did say that the fuel bowl is commonly empty due to evaporation after a few days (the additives in newer fuels he says??).
So I took the top of the carb off today and removed the accel. pump. It looked perfect consistent with a recently rebuilt carb.
THE FUEL BOWL was EMPTY. So obviously thats part of the problem. ?evaporation or leak.
But, when I filled the bowl with gas, still no pump squirt. Weird. Looked at the accel pump again and put on a new seal. No squirt. Put it back together and drove it. No stumble on acceleration.
Bizzaro. I love workin' on old cars.
One other thing I noticed is that the air horn seemed warped which according to Lars is another common problem. It's not terrible, but maybe it could be related.
Fire away with your thoughts Gentlemen...
Melting Slicks
Joined: Mar 2009
Posts: 3,126
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The fact that you have no major stumble under acceleration is unusual if no shot of fuel. If there is no shot after driving car and removing air cleaner top the only thing that I could suggest you check is the acc. pump check ball. It is under a screw in the bottom of the float bowl. If stuck it could cause your problem. Are discharge nozzles open? On my car if you move linkage after driving car and car warmed up, a cloud of vaporized fuel will come up out of primaries and it can be seen and heard so acc. pump operation is apparent. When it sits for a week or two the bowl goes dry. If only a day or two it starts right up. Good luck, mds... 
Last edited by mds3013; Mar 10, 2010 at 07:40 PM.
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
The fact that you have no major stumble under acceleration is unusual if no shot of fuel. If there is no shot after driving car and removing air cleaner top the only thing that I could suggest you check is the acc. pump check ball. It is under a screw in the bottom of the float bowl. If stuck it could cause your problem. Are discharge nozzles open? On my car if you move linkage after driving car and car warmed up, a cloud of vaporized fuel will come up out of primaries and it can be seen and heard so acc. pump operation is apparent. When it sits for a week or two the bowl goes dry. If only a day or two it starts right up. Good luck, mds...
Where are the accelerator pump discharge ports? Are they up high in the air horn or deeper down near the throttle plate?
I guess if I remain stumped I'll just have to take it off, box it up and send it to the Carburetor man with a note to send back when the accelerator pump squirts again, and while your at it check those well plugs...
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
I do not think you will have to send it back. The guys on the forum can probably get you through it. The ports are on the air horn, the top piece. They direct the fuel directely onto the boosters, the round rings in the primaries. What I would do if I had your carb in my hands is remove top, fill the pump well with fuel, place pump in well and push down. Fuel should come out of holes toward center of main body in front of primaries that then sends fuel out of holes in top. Make sure you are careful with raw fuel around a hot engine. mds...
Last edited by mds3013; Mar 10, 2010 at 10:08 PM.
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
thanks for the help mds
I did just that today, I took of the air horn and seeing the fuel bowl empty I filled it and pump well and pushed down on the pump plunger.
Fuel barely trickled out of the holes you speak of. No force and very little volume, just a slight dribble. That's when I replaced the cup/seal on the pump even though it looked fine. Made no difference.
I did just that today, I took of the air horn and seeing the fuel bowl empty I filled it and pump well and pushed down on the pump plunger.
Fuel barely trickled out of the holes you speak of. No force and very little volume, just a slight dribble. That's when I replaced the cup/seal on the pump even though it looked fine. Made no difference.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
OK. On the side of the well there is a refill slot. Does the pump seal rise above it when in the full up position? It should not. This is how the well refills but fuel gets to bottom of well past the acc. pump cup on up stroke. Check to see if check ball is in place and not stuck. It is under the screw in bottom of float bowl. No gasket on screw but it should have a pin, part of screw, that keeps check ball in proper position. mds...
Last edited by mds3013; Mar 10, 2010 at 11:15 PM. Reason: left out info
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
OK. On the side of the well there is a refill slot. Does the pump seal rise above it when in the full up position? This is how the well refills. Check to see if check ball is in place and not stuck. It is under the screw in bottom of float bowl. No gasket on screw but it should have a pin, part of screw, that keeps check ball in proper position. mds...
as soon as I get free time I'll take the air horn off again and check the refill slot and check ball
thanks
Race Director
Joined: Apr 2007
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From: Henderson Nv-Rohnert Park/Sonoma C o. ca/born in NY Rockaway Beach.
I just had the same kinda issue. I was told that the costco gas i was using in the car is the worst gas to be using.. all of the extra crap they put in that gas is just eating away at the plastic in the carb.. Im not sure what this part is called but it was just being eaten away from the alcohol and the gas was seeping through causing all kinds of issues.. you can see in the pic on is a little bigger than the other and a little off colored ..
This is a brand new motor and a brand new carb rebuild.. happened in less than 2000 miles..
Not sure if this helps at all. but just thought id share.
This is a brand new motor and a brand new carb rebuild.. happened in less than 2000 miles..
Not sure if this helps at all. but just thought id share.
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
well I took off the air horn again today and noticed that the new pump seal/cup was slighter smaller, in that the cup sides were not as "tall". The old pump seal looked new, but I replaced it with the new shorter seal.
Now it's fixed and I can see a nice squirt of gas into each venturi!
Maybe the tall sided seal didn't allow the pump well to refill. That's my theory.
Car runs 100% better. hooray!
Now it's fixed and I can see a nice squirt of gas into each venturi!
Maybe the tall sided seal didn't allow the pump well to refill. That's my theory.
Car runs 100% better. hooray!
Tech Contributor
Joined: Aug 1999
Posts: 14,379
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From: At my Bar drinking and wrenching in Lafayette Colorado
As stated above, leaking well plugs are very rare: I have come across 2 in the last 700 rebuilds I have done. This is not to say yours can't be leaking. It is actually more common to have a porous or cracked float bowl than to have leaking well plugs.
You can very easily test for leakage: Remove the carb from the engine and wipe it off to make sure it's dry on all bottom surfaces. Set it up on some tall sockets on your workbench with the airhorn removed. Fill the float bowl with solvent (lacquer thinner, alcohol, or gasoline) up to the level of the needle/seat and let it sit. After a few minutes, inspect the bottom of the carb for wetness, dripping and leakage - if the bowl is going dry overnight, there would be a visible drip if it's leaking out the bottom of the float bowl.
Chances are greater that you have a bad fuel pump checkvalve: Since the Q-Jet needle/seat sits in the bottom of the float bowl, a bad fuel pump checkvalve will cause fuel to be siphoned out of the float bowl when the standing column of fuel between the pump and the carb drops down. If you do not have leakage out of the bottom of the bowl, this is likely happening in addition to the evaporation. You can correct this is one of several ways:
Lars
You can very easily test for leakage: Remove the carb from the engine and wipe it off to make sure it's dry on all bottom surfaces. Set it up on some tall sockets on your workbench with the airhorn removed. Fill the float bowl with solvent (lacquer thinner, alcohol, or gasoline) up to the level of the needle/seat and let it sit. After a few minutes, inspect the bottom of the carb for wetness, dripping and leakage - if the bowl is going dry overnight, there would be a visible drip if it's leaking out the bottom of the float bowl.
Chances are greater that you have a bad fuel pump checkvalve: Since the Q-Jet needle/seat sits in the bottom of the float bowl, a bad fuel pump checkvalve will cause fuel to be siphoned out of the float bowl when the standing column of fuel between the pump and the carb drops down. If you do not have leakage out of the bottom of the bowl, this is likely happening in addition to the evaporation. You can correct this is one of several ways:
- Install a good GM/Delco fuel pump with a good check valve.
- Remove the needle float clip from the needle so the needle blocks the seat when fuel pressure drops to -0-.
- Install a seat without the "windows" so fuel cannot be siphoned from the bowl.
- Install a checkvalve inlet filter, NAPA part number 23051 for the short filter or 23052 for the long filter.
Lars
