Q-jet siphon problem
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,125
Likes: 9
From: Crescent City, CA
Q-jet siphon problem
Is there a check valve or something that stops the gas from siphoning out of the carb. I would think it would be in the filter area.
After the car sits for a couple of days the carb is empty of gas. After cranking a short while it starts, and then starts on first crank.
What am I missing?
Thanks for any advise.
Terry
After the car sits for a couple of days the carb is empty of gas. After cranking a short while it starts, and then starts on first crank.
What am I missing?
Thanks for any advise.
Terry
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
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Re: Q-jet siphon problem (trw)
Maybe one of two things.
Yes many of the stock fuel filters on a Q-jet had a check valve made into the end of it just for that purpose. Some aftermarket ones leave it off. Look at it and see if there is a little rubber looking plug on one end. You do still have the spring in there don't you?
The second is that with time many Q-jets leak from the "well plugs" in the bottom of the carb bowl. The fix is basically to clean them real well and use JB weld to epoxy over them on the bottom side.
The clue can be "does it smoke a lot" when it is first started like it is flooded? If plugs are leaking, all the gas goes down into the intake and acts flooded. if it is syphoning out of bowl, it runs clean after it starts, it just acts like it has run out of gas.
JIM
Yes many of the stock fuel filters on a Q-jet had a check valve made into the end of it just for that purpose. Some aftermarket ones leave it off. Look at it and see if there is a little rubber looking plug on one end. You do still have the spring in there don't you?
The second is that with time many Q-jets leak from the "well plugs" in the bottom of the carb bowl. The fix is basically to clean them real well and use JB weld to epoxy over them on the bottom side.
The clue can be "does it smoke a lot" when it is first started like it is flooded? If plugs are leaking, all the gas goes down into the intake and acts flooded. if it is syphoning out of bowl, it runs clean after it starts, it just acts like it has run out of gas.
JIM
Racer
Joined: Sep 2002
Posts: 392
Likes: 0
From: Iowa
Re: Q-jet siphon problem (trw)
The check valve is part of the filter. My car does the same thing and I installed a new filter/check valve so I don't think that is the problem. There are some well plugs inside the carb that leak and need to be sealed (search the carb papers by Lars also the Q jet manual (sorry don't remember the name) has the info also). I sealed the plugs with epoxy but still have the problem :confused: A friend told me he sealed his with epoxy but it didn't help, he then used a fuel tank sealant and the problem went away.
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,125
Likes: 9
From: Crescent City, CA
Re: Q-jet siphon problem (427Hotrod)
Hotrod
I rebuilt the carb about a year ago and JB'ed the plugs. It has always done this. I am using AC GF 427 fuel filters.They are open at one end and solid at the other. Could it be leaking back through the solid end (no gasket). Is there a gasket on that end of the filter?
No smoking on start-up. That stopped when I JB'ed the plugs.
Starts like it is out of gas, which it is!!!
Thanks
Terry
I rebuilt the carb about a year ago and JB'ed the plugs. It has always done this. I am using AC GF 427 fuel filters.They are open at one end and solid at the other. Could it be leaking back through the solid end (no gasket). Is there a gasket on that end of the filter?
No smoking on start-up. That stopped when I JB'ed the plugs.
Starts like it is out of gas, which it is!!!
Thanks
Terry
Racer
Joined: Sep 2002
Posts: 392
Likes: 0
From: Iowa
Re: Q-jet siphon problem (trw)
Well I am wondering if either the accel pump is leaking down, has a bad seal, or the fuel is evaporating after a log sit on top of a hot manifold :confused: I wish I could find the problem I rebuilt the carb last winter as you did so we shouldn't be having this problem. :banghead:
Anyone else have any ideas???
Anyone else have any ideas???
Race Director
Joined: Jan 2000
Posts: 13,014
Likes: 2,257
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Re: Q-jet siphon problem (trw)
The anti-siphon check valve looks like a little rubber deal that pushes into the inlet of the filter itself. It has a small spring in it. I remember from way back when folks having this issue when they installed the wrong filter. Correct one always fixed the problem.
Not sure why epoxy didn't seal some of the carbs. It's always worked for me, never had one leak.
JIM
Not sure why epoxy didn't seal some of the carbs. It's always worked for me, never had one leak.
JIM
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