Quadrajet Accelerator pump issue
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
Intermediate
Joined: May 2007
Posts: 48
Likes: 2
From: Reading PA
When you say remove the needle clip, you do mean permanently correct? I also have the same hard starting problem after sitting a few days. I’ll also be changing to the NAPA filter and windowless seat. Thanks for the help.
Dean
Dean
Race Director
Joined: May 2006
Posts: 18,660
Likes: 2,562
yes they mean permanently. As the gas drops due to evaporation the float drops pulls up on the needle because it's clipped and the drainback occurs. With no clip as the float drops the needle stays seated and prevents the drainback.
Thread Starter
Racer
Joined: Nov 2009
Posts: 384
Likes: 2
From: Tulsa OK
Thanks Lars
extremely helpful, accurate and precise, as usual.
You are truly one of the jewels of this forum.
FW
extremely helpful, accurate and precise, as usual.
You are truly one of the jewels of this forum.
FW
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
Heel & Toe
Joined: May 2001
Posts: 21
Likes: 0
From: In the garage working on the Vette Ontario
So.... I have the same problem.
Weather has turned nice here in Ontario so figured I'd start up the Vette and take her out of the garage.
After numerous attempts to start my baby I turned to corvetteforum and found your thread.
No fuel getting into carb but fuel pump working fine.
I took the top plate off the carb and replaced acclerater pump seal and top plate gasket.
Car ran fine for 20 seconds until bowl emptied obviously but wouldn't refill.
Accelerater check valve possibly?
If so, I'll just take the whole dam thing off and start over.
Any other ideas?
Cheers.
Jon
Weather has turned nice here in Ontario so figured I'd start up the Vette and take her out of the garage.
After numerous attempts to start my baby I turned to corvetteforum and found your thread.
No fuel getting into carb but fuel pump working fine.
I took the top plate off the carb and replaced acclerater pump seal and top plate gasket.
Car ran fine for 20 seconds until bowl emptied obviously but wouldn't refill.
Accelerater check valve possibly?
If so, I'll just take the whole dam thing off and start over.
Any other ideas?
Cheers.
Jon
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,361
From: At my Bar drinking and wrenching in Lafayette Colorado
If the fuel pump is working but no fuel is getting into the carb, you either have a completely plugged filter or a jammed needle/seat. The filter and the needle/seat are the only two components between the pump and the float bowl. There is no accel pump component that can prevent fuel from getting into the carb.
Lars
Lars
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Heel & Toe
Joined: May 2001
Posts: 21
Likes: 0
From: In the garage working on the Vette Ontario
Lars,
I hear you're the best so I'm hoping you can help.
Actually took the fuel filter out as I thought that might be the problem but to no avail. Lots of fuel pumping.
The needle/seat was in my opinion fine last fall when I put the car away so should have been fine now. Saying that, after taking top plate off and repairing acc pump seal, I may not have properly seated needle but doubt it.
Any other ideas?
Cheers,
Jon
I hear you're the best so I'm hoping you can help.
Actually took the fuel filter out as I thought that might be the problem but to no avail. Lots of fuel pumping.
The needle/seat was in my opinion fine last fall when I put the car away so should have been fine now. Saying that, after taking top plate off and repairing acc pump seal, I may not have properly seated needle but doubt it.
Any other ideas?
Cheers,
Jon
Heel & Toe
Joined: May 2001
Posts: 21
Likes: 0
From: In the garage working on the Vette Ontario
Here's my update peeps,
Lars was once again correct.
Took top plate off once again and found that my needle/seat was indeed sticking. Cleaned it and ta da, lots of fuel getting into carb and my baby started up
and is now basking in the spring sunshine as opposed to the flourescent glow of the garage.
Thanks again Lars.
Jon
Lars was once again correct.
Took top plate off once again and found that my needle/seat was indeed sticking. Cleaned it and ta da, lots of fuel getting into carb and my baby started up
and is now basking in the spring sunshine as opposed to the flourescent glow of the garage.Thanks again Lars.
Jon
