Author Topic: Quadrajet well plugs leaking  (Read 3420 times)

Online Rapid Roy

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Quadrajet well plugs leaking
« on: August 05, 2018, 12:28:44 PM »
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. 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. Also took longer to start. Now to decide to go back to last shop that rebuilt it 13 months ago or go another route. 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.

Any suggestions?

TIA
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
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Offline Henry

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Re: Quadrajet well plugs leaking
« Reply #1 on: August 05, 2018, 12:49:55 PM »
Hi Rapid Roy:
Are you sure it is just not bowl evaporation due to sitting a long time inactive in the extreme Texas heat? If the well plugs were leaking you would also be getting problems like stalling after driving a while or hard starting when the engine is hot after a drive.
Regards,
Henry

Online Rapid Roy

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Re: Quadrajet well plugs leaking
« Reply #2 on: August 05, 2018, 04:46:55 PM »
I really don't think it is evaporation. Truck is parked under awning and in shade all time when I'm not driving. Besides, the temp was not over 100 both weeks. If the bowl had plenty of fuel, then I would have seen stronger stream of fuel when watching and operating pump.
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline VileZambonie

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Re: Quadrajet well plugs leaking
« Reply #3 on: August 05, 2018, 08:15:38 PM »
Agreed, leaking well plugs will give you a fuel fouled hard start. An extended cranking condition may be a combination of issues, nevertheless sealing the well plugs is a simple task.
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Online Rapid Roy

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Re: Quadrajet well plugs leaking
« Reply #4 on: August 05, 2018, 08:35:22 PM »
Agreed, leaking well plugs will give you a fuel fouled hard start. An extended cranking condition may be a combination of issues, nevertheless sealing the well plugs is a simple task.

I have had no experience doing it myself. Probably the primaries are leaking. I could see them on the bottom when it was rebuilt. Can these be resealed without disassembling carb? I have read JB Weld is best, not sure. I would rather not  disassemble myself. What would be procedure to reseal?
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline Monkey Uncle

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Re: Quadrajet well plugs leaking
« Reply #5 on: August 06, 2018, 05:36:05 AM »
It may or may not be the well plugs.  I rebuilt my Qjet recently and used JB marine weld to seal all of the well plugs.  I still had issues with the fuel level declining and hard starting after sitting for a couple of days.  I figured the epoxy didn't hold, but when I pulled the carb back off and leak tested it on the stand, I found no leaks.  I still haven't done a final fix on it yet, but after lots of testing and observing the fuel level decline, I am pretty sure the fuel is siphoning out through the fuel inlet.  I'm planning on removing the needle clip next time I have the carb off, so that the needle doesn't un-seat after shut down and allow fuel to siphon out.  We'll see if that works.

If you do re-seal the plugs, the JB marine weld claims to be resistant to heat and fuel.  I'm guessing the other formulations of JB weld would not hold up.
« Last Edit: August 06, 2018, 05:38:10 AM by Monkey Uncle »

Online Rapid Roy

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Re: Quadrajet well plugs leaking
« Reply #6 on: August 06, 2018, 06:49:26 AM »
I am pretty sure the fuel is siphoning out through the fuel inlet.

That was another thought I have had. I really thought fuel inlet was a little higher than fuel bowl. I did get a check valve but haven't installed yet till I really thought fuel drain back was happening. May need to install anyway just to eliminate possibility.
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline Monkey Uncle

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Re: Quadrajet well plugs leaking
« Reply #7 on: August 06, 2018, 01:26:06 PM »
I am pretty sure the fuel is siphoning out through the fuel inlet.

That was another thought I have had. I really thought fuel inlet was a little higher than fuel bowl. I did get a check valve but haven't installed yet till I really thought fuel drain back was happening. May need to install anyway just to eliminate possibility.

The inlet is higher than the bottom of the bowl, but lower than the fuel level when the bowl is full.  If you have one of the needle seats with the window in it, the effective opening is a little lower than with the non-windowed seat.  Siphoning won't completely drain the bowl, but it will draw it down low enough to where the engine won't start unless you crank for a little while to refill the bowl.

Offline Henry

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Re: Quadrajet well plugs leaking
« Reply #8 on: August 06, 2018, 01:41:44 PM »
Hi Roy:
Do you have hard starting both cold engine and hot engine? Has it been this way for a while or is this a recent phenomenon? Do you have leaking around your carb gaskets? What model of Q-jet do you have? Another common test for welch plug leaking is to prop open the throttle and air horn butterflies (on a hot or cold engine) and observe if the floor of the manifold is completely wet...if it is, then your welch plugs are leaking.

Unfortunately, to get a good adhesive seal on the welch plugs, you have to clean all the old fuel out of the carb...it has to be clean and dry on both sides of the welch plugs before  applying adhesive. JB weld is OK as long as it is the version for aluminum bonding...I would recommend you use the stuff Monkey Uncle mentioned. Also, I have heard of a permanent fix which is to bond in threaded plugs...but this is a big undertaking if you dont have all the right tools and experience in tapping and fabricating threaded aluminum or bronze plugs. I have not heard of anyone successfully welding or brazing the holes shut and this may because the castings are of die cast aluminum with a lot of silicon content that is not amenable to this process.

Maybe a first step is to just take off the air horn and make sure everything is clean and operates properly in the top of the carb and close it back up and see what happens.

Regards,
Henry