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Subject: Carb. leak-down

Original Message
Name: Phil
Date: February 19, 1998 at 19:14:22
Subject: Carb. leak-down
Comment:
The previous "fuel drainage" question has prompted this one. I have a 67 396 w/Quadrajet. After sitting for a while (couple of days), I have to prime the carb before it will fire up. I have never run the engine with this carb before. I was given the carb with the engine and rebuilt & installed it when I rebuilt the engine. There is no externally visible signs of fuel leakage from linea or carb gaskets. I have a "see-through" fuel filter behind the fuel pump and it is staying full.

I have read other postings concerng Quadrajets that make mention of ways that fuel can leak out of the bowls and down into the intake while sitting. Is this where I should look? The car is still a garage queen so I can't tell you how the car is running on the road. I just start it every month or so to keep things oiled.

Thanks,

Phil


Response Number 1
Name: Steve S
Date: February 20, 1998 at 07:25:15
Subject: Carb. leak-down
Reply:
Sounds like the well plugs are leaking or maybe a warped bottom plate. Well plugs leaking are a common problem with Q-jets. The manufacturing process required holed to be drilled then filled with a plug to seal the bowls. I beleive you can get repair kits. Most rebuild kits have a rubber gasket that covers them but I have found they do not cure the problem. Q-jets all look very simular externaly but are very different internaly. If you could verify that this is the correct Q-jet for the engine I would have it fixed. I personnal like Q-jet performance when they are set up right. I hope this helps.

Response Number 2
Name: Steve S
Date: February 20, 1998 at 08:19:48
Subject: Carb. leak-down
Reply:
Sounds like you make have leaking well plugs or maybe a warpped base plate. The manufacturing process requires holes to be drilled then filled with plugs to seal the bowl. Most rebuild kits come with a spongy gasket to cover these plugs but I found that they do not seal. I think you can get well plug repair kits. A lot of Q-jets look alike outside but are very different inside. If you can verify that this is the right one for your engine I would definately repair it. I personnal like the Q-jet performance.

Response Number 3
Name: tom
Date: February 20, 1998 at 15:35:07
Subject: Carb. leak-down
Reply:
Phil; Been through this a couple of times. Sometimes is is leaking core plugs. Most rebuild kits have a sealer pad that installs under the jet well that fixes this. But, I have had 2 carbs that this didn't fix. I have found out that this is caused by porosity in the metal itself in the bottom of the fuel bowl. There is no fix for this as far as I know. I just intalled an electric pump to prime the carb after sitting for a few days. Tom

Response Number 4
Name: Nick
Date: February 20, 1998 at 22:01:06
Subject: Carb. leak-down
Reply:

One easy way to fix the well plugs is to cover them with epoxy. I do this every time I rebuild a Quadrajet, and have not had any problem with this since.

Response Number 5
Name: Phil
Date: February 21, 1998 at 08:05:44
Subject: Carb. leak-down
Reply:
Thanks for the considerate replys. The carb is not original to this engine. I guess it is worth opening up and re-sealing the well holes. I have both, some 2-part epoxy and JB Weld. Which would be better? If this doesn't work, I figured that I would just buy a new carb.

The engine is basically a stock 396/325 HP unit. It is bored .040 and I installed a Comp. Cams "268" cam. The car will only be a weekend driver/stop light racer. If the above fix doesn't work, I had thought of getting a new Edelbrock Q-Jet as a replacement. Any thoughts? I do plan on showing the car some but am not planning on trying to win anything for complete originality even though I want to keep it as stock looking as possible.

Thanks,

Phil


Response Number 6
Name: Schurkey
Date: February 22, 1998 at 13:37:14
Subject: Carb. leak-down
Reply:
One thing not mentioned: Q-junks do leak down from the well plugs-and epoxy does a fine job of sealing this. BUT if the fuel level drops in the float bowl, the float drops and the needle and seat open. If the fuel pump check valves have an imperfect seal, the fuel will siphon back to the level of the fuel tank. It will take a while to re-fill the float bowl as the pump has to first re-fill the fuel tube up to the carb. The backyard mechanic's fix for this is to buy a stock type paper fuel filter that has the little plastic (rollover safety) valve stuck in the inlet. These are cheap and common. (If your fuel filter is between the pump and carb, fairly high on the engine, and it is staying full, indicating good fuel pump check valves this tip may not help you.)

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