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Old 08-05-2018, 08:07 PM   #1
Bandit130
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Quadrajet well plugs leaking

Carb fuel bowl leaking down which I am sure it is the well plugs. Week before last, did not drive truck for 5 days. Did not plan it, just happened that way. Took longer to start up than usual. Last week intentionally did not drive for 6 days, looked in carb and manually operated accelerator about 4 or 5 times and only saw 2 spits of gas, no stream. Also took longer to start. Now to decide to go back to last shop that rebuilt it 13 months ago or go another route, maybe change to Edelbrock 1405 or 1406. I am sure he will not warranty that due to time. It was rebuilt professionally, well, carbs and throttle bodies are all they repair.

Is there any permanent fix for the leaking. Seems to be a common issue with quadrajets. I do not know the reason for them to be manufactured that way, but there could be a logical reason.

(I switched a Holley 750 cfm on my former 72 that PO had installed to Edelbrock 1406, bought used, rebuilt it myself and worked great.

Any suggestions?

TIA
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Old 08-05-2018, 10:28 PM   #2
geezer#99
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Re: Quadrajet well plugs leaking

The well plugs plug off machining passages in the carb.
Best cure is with this kit from Cliff.

https://cliffshighperformance.com/Qu...ottom-plug-kit

A carb rebuilder wouldn’t likely plug them. Not part of the rebuilding process. Some might smear a little epoxy on them and hope it’s good enough.
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Old 08-06-2018, 07:34 AM   #3
Getter-Done
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Re: Quadrajet well plugs leaking

Seal-All Household sealant works (a little while)but probably not as good as that kit from Cliff
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Old 08-06-2018, 09:11 AM   #4
CSHADES
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Re: Quadrajet well plugs leaking

I have had good luck with lightly sand blasting the plugs and then a bit of JB weld over them and let it sit over night before reassemble. Plow truck has been done for 5 years with no problems and have fixed some customer q-jets with out problems.
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Old 08-06-2018, 10:57 AM   #5
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Re: Quadrajet well plugs leaking

It all sounds pretty normal to me. When my vehicles sit for a week they take longer to start whether Qjet or Eddy. (fuel injection has spoiled us) I figure gas just evaporates. After the long first start, they will fire right up the rest of the day or the next couple days. Every time I rebuild a Qjet I will fill it with gas and set it on a newspaper on the bench over night and never had one leak out the well plugs. I figured it was an urban legend kinda thing.
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Old 08-06-2018, 11:48 AM   #6
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Re: Quadrajet well plugs leaking

If the rebuilder didn't at least make an attempt at sealing the well plugs while the carb was apart, IMO negligence on his/her part. Well known issue for decades. I bought carb rebuild kits in the late 70's that included that little foam pad as a 'fix' for the problem. The pads didn't last long, but even then, the problem was known.

As mentioned, evaporation is your enemy for long term sitting. The bowls on these carbs, either Q-jets or Eddys, are basically open vent to the atmosphere. The gas will disappear after a few days due to simple evaporation. Another place it can go is back out the gas inlet and down to the fuel pump.

More then a few days of sitting, especially if it was parked hot, will empty the bowl even with no leaks. If you still some gas in there after 6 days, count yourself lucky. Especially Texas in summer.
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Old 08-06-2018, 11:51 AM   #7
geezer#99
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Re: Quadrajet well plugs leaking

They’ll never Leak like that Al.
You need to get the carb hot.
Like when you shut it down and it heat soaks.
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Old 08-06-2018, 04:30 PM   #8
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Re: Quadrajet well plugs leaking

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Originally Posted by Dead Parrot View Post
....back out the gas inlet and down to the fuel pump.

More then a few days of sitting, especially if it was parked hot, will empty the bowl even with no leaks. If you still some gas in there after 6 days, count yourself lucky. Especially Texas in summer.
Recently rebuilt the Q-jet in the truck I just got, but have not driven yet, and noticed that it fires up immediately after having run, but the bowl completely empties if it sits for a week and needs to be manually filled so I don't sit there cranking it 'til it fills. The well plugs were sealed, so I'm sure that's not the problem. I'm going with the fuel running back down the feed line; the truck came with a plastic universal inline filter spliced into the hard line and the check-valved internal filter removed.
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Old 08-06-2018, 11:30 PM   #9
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Re: Quadrajet well plugs leaking

Hygrade Jiffy Kit has a kit with two new plugs w/ o-rings on them & the foam pad to keep them pushed up into the wells, I've used a pile of them & they work great.
https://www.ebay.com/p/Hygrade-Roche...0168222&chn=ps
One problem our trucks run into when using a carb after installing a high speed gear set in the rear end the engine starts to cruise at a much lower rpm, and also a much lower manifold vacuum. Then the power enrichment spring doesn't match the manifold vacuum anymore & the carb thinks the truck is towing a camper w/ you Maw N Law in it up a hill & opens the power circuit, bypassing the jets.
That's when you have to have a hand full of springs & a vacuum gauge to TRY & tune for optimum cruise vacuum.
Sometimes high speed rear axles & carbs just can't match what a MPFI engine can do!
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Old 08-07-2018, 08:29 AM   #10
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Re: Quadrajet well plugs leaking

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Originally Posted by geezer#99 View Post
They’ll never Leak like that Al.
You need to get the carb hot.
Like when you shut it down and it heat soaks.
I'll take your word for it Geezer. I always figured a leak was a leak. I can literally watch the fuel boil in my clear fuel filter in hot weather. I'm sure it is doing the same thing inside the carb and that is helping the evaporation process.

I used to give my plow truck a shot of gas to start it so I wouldn't wear out my starter. Then I spun a bearing and figured it is better to turn the starter and let the oil pressure build before it starts. Having the truck fire up instantly before it had oil pressure probably wasn't good for my crank bearings. I haven't timed it but in around 5-8 seconds of cranking I have oil pressure and fuel in the fuel filter/carb. The rest of the day it starts in 1 second. Those gear reduction starter really whirl the engine a lot faster too.
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Old 08-07-2018, 08:40 AM   #11
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Re: Quadrajet well plugs leaking

Just to clear it up Al, it wasn’t my original thought on the heat to leak concept. I read about it somewhere in cliff’s web site. It makes sense though.
Fuel boiling in the filter is much nicer to see than fuel boiling on the intake. You don’t want to experience that more than once in a lifetime! I think I lost 10 years when I saw it!
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Old 08-07-2018, 10:19 AM   #12
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Re: Quadrajet well plugs leaking

If you aren't running an original style fuel filter in the carb inlet, the fuel will drain back out too. Those filters are supposed to have some sort of anti drain back on them to help keep the bowls full.
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Old 08-10-2018, 03:41 PM   #13
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Re: Quadrajet well plugs leaking

I used the kit from Cliff's on the Q-jet in my 454 and it made a world of difference.

The carb would leak down over a couple of days before.
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Old 08-10-2018, 06:14 PM   #14
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Re: Quadrajet well plugs leaking

Have been investigating a little further and not 100% sure it is well plugs or fuel draining back toward tank. When jwilson645 mentioned original fuel filter that has a check valve, I remembered when I got truck 3 years ago was doing tuneup and gathering parts and auto parts store did not have filter with one. Did not realize at that time it may be critical so got one without. I usually drive several days a week and had not been very noticeable until it sat for 5 days. So, I have ordered check valve for original filter and will see next week if that is the issue. I had purchased an inline check valve and had not installed yet.
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Old 08-10-2018, 06:33 PM   #15
truckin 79
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Re: Quadrajet well plugs leaking

The original q-jet is a paper filter I dont know how that would be a anti drain back valve feature. I battled hard starts for a while and when I replaced fuel filter that helped get fuel into bowl quicker after pumping the gas pedal a couple times. I am not saying it will not work just saying those threads on filter housing strip out so easily.
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Old 08-10-2018, 07:46 PM   #16
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Re: Quadrajet well plugs leaking

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Originally Posted by truckin 79 View Post
The original q-jet is a paper filter I dont know how that would be a anti drain back valve feature. I battled hard starts for a while and when I replaced fuel filter that helped get fuel into bowl quicker after pumping the gas pedal a couple times. I am not saying it will not work just saying those threads on filter housing strip out so easily.
The check valve is small and fits into filter. Some filters come with or without. You can see it here.

https://www.ebay.com/itm/Quadrajet-f...72.m2749.l2648
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Old 08-12-2018, 12:34 AM   #17
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Re: Quadrajet well plugs leaking

That check valve looks like a serious fuel restriction to me!
If some yall think the fuel in the carb is draining back to the tank, please explain how the fuel in the carb bowl can push the float & needle up, get up & over into the seat inlet openings, down past two check valves in the fuel pump & then up & over into the tank.
Maybe the fuel could heat & expand enough to raise the float up.
It would be a simple test to take the inlet line loose from the pump & set a receptacle under it after the initial flood of gasoline & then watch it.
Q jets don't hold very much fuel in the bowls to begin with & any leak drains them fast.
I'v had lots trouble with diesel engines having fuel drain back but never a gasoline engine.

Last edited by andyh1956; 08-12-2018 at 12:47 AM.
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