Quadrajet rebuild

[JerryIndy2112]

I bought my 71 in November. I smell gas around it parked. There has even been leakage that is destroying my old asphalt driveway. Looking under the truck, all rubber is shot. Cab mounts. Front end rubber. All gaskets leak from engine to rear end. Oil leaking at every point. I bought to to restore, so it is expected from a truck built almost 50 years ago. She is so sexy, so I will deal with it. The thing to do is to do a project one at a time. Don't let it overwhelm you. Right now it is in my tiny garage, on jack stands. Front brakes were locking up on my weekend drives. Make it safe. Doing front bearings. Have ordered rotors, seals, calipers, pads. While it is in garage I pulled carb. The well seals? Well they are leaking. Watched rebuild videos on youtube. Checked some sources. One guy says cover it with JB weld. Another says it will only last a week. My rebuild kit is on the way. What have people tried? What worked long term. I have the carb in hand and the ones I can see are missing the "weld" that was factory. I know the guys here have experience with the carb issue. So what is best way to seal this during rebuild?

Thanks, Jerry

[sick472]

Do some research on drilling and tapping the primaries with 10-32 x 1/4" countersunk allen head screws (along with the JBweld or epoxy) and I believe Echlin kits come with a rubber seal for the secondaries.

I would, first, bench test the carb to make sure that is the problem before betting on the well plugs in case you have not done so. These plugs are often suspected of leak-down problems to find that the internal pump, filter (without check valve or faulty one), and/or high ethanol fuels are to blame.

[geezer#99]

You need a seal kit like this.
https://cliffshighperformance.com/Qu...ottom-plug-kit

[68Gold/white]

Originally Posted by geezer#99

you need a seal kit like this.
https://cliffshighperformance.com/qu...ottom-plug-kit

x2!!!!!!

[54blackhornet]

Jerry sounds like you have a list of projects to tackle, after numerous attempts at rebuilding my Qjet unsuccessfully I finally sent it out for rebuilding, Now it runs great but still leaks down after sitting for a day or two ? The well plugs where resealed with epoxy.

[JerryIndy2112]

thanks for the replies. I rebuilt a carb for a Toyota some 35 years ago. I am not afraid to do the work myself. As far as weather it is the issue. I can see the original putty or whatever was originally used has come off of one and fell off the other when carb was pulled. So to me, fix it while I am in there. I have not opened carb up yet, but I think the same is most likely true of the other 2 inside. Besides, I can't see taking it all apart for a rebuild and not fixing it anyway. The truck is a 71 but the carb is a 73. It is still very old, with a lot of miles on it. Make it right, is my opinion. I think I will most likely use the putty posted. I will sleep better knowing that an issue is solved

Jerry

[jamyers]

I've dealt with Q-jets for decades now, and still like them better than any other carb. That said, I've never had success sealing those wells with anything other than drilling/tapping/threaded plugs. I'm not sure how gas-resistant Marine-Tex is, but I've used the fuel-resistant locktite permanent threadlocker with good results.

Don't let it scare you, it's easy if you take your time and think about what you're doing.

[Steeveedee]

Before you get it apart, make sure that the throttle shafts arent's leaking vacuum. You can have that done by a local carb shop, as I did, because I didn't want to send it out across the country (to Cliff Ruggles) for a simple repair that could be done locally. I did buy the rebuild kit from Cliff, because I needed parts that don't come in the (regular) auto parts store kits. The secondary metering rod cam broke on mine, so when the secondaries opened, it just died from lack of fuel. I've never seen a kit with that cam in it. Runs like a champ now, and it is the original carburetor from 1970.

[JerryIndy2112]

Ok, so I know this site is a great resource for all this information. I have a question. Why did they design a carb that has something that needs to be sealed? I mean why even design it that way? Is there a reason you may want them to leak? It seems that this carb has 4 points that need to be sealed. Why even have any hole there? Am I correct in my assumption that these factory seals were on purpose? Is there a reason to not seal them? I have seen too many issues with other carbs that members have had by just cruising the forum. So I am willing to keep the quadrajet. It was used for decades, people know them, there are resources out there. I work in HVAC. Sometimes things are designed a certain way because of the history or evolution of design. If you understand that you can many times get to the root of an issue. My question is why even have 4 points sealed in the factory to make it work right? Why not make the mold, not have those points any more? Maybe no one here designed this carb, but maybe several people know the story by experience.
I have ordered the marine sealer. I assume you just cover the 4 points. Am I still missing something?
Thanks, I am just a curious person. I would like to know why I need to seal this. What is the history? I am restoring a cool old truck. I expect some hard work. Some learning. Some ups and downs.

Jerry

[geezer#99]

Simply put, it’s access!
Access holes need to be there so the internal passages can be drilled out.
Passages for vacuum ports, jets, accelerator pump etc.
All the internal stuff.
Making a mold would be far more complicated than just having access holes.
The well plugs didn’t leak until after many heat cycles and a lot of miles.
At least there’s better cures now.

[Steeveedee]

Like Geezer says, except that the mold has to have places for things to be installed after the casting is finished. In general, the manufacturers were required to have replacement service parts available for 7 years after the manufacture date. Given that you are working on a vehicle that is way past that date, you have to understand that things are going to be worn out and/or leaking. The wearing out and leaky part is already decades old, but still well beyond the expected lifetime of the vehicle.

[Greasey Harley]

Originally Posted by sick472

...i would, first, bench test the carb to make sure that is the problem before betting on the well plugs in case you have not done so. These plugs are often suspected of leak-down problems to find that the internal pump, filter (without check valve or faulty one), and/or high ethanol fuels are to blame.

X2 !!

Q-Jets manufactured after 1967 have an "almost ZERO" rate of well plugs failing. believe it or not

To test the well plugs, turn the bare casting upside down, so the well plugs are on the top.
Mist the well plugs with a soapy water solution, and blow high pressure air from underneath.
if the plugs leak, you will see bubbles.
No bubbles ----------> No leak.
No leak ---------> No repair needed

If you see bubbles, I recommend getting a different Q-jet to rebuild, as it will be cheaper and easier than repairing a unit with leaky well plugs.
The only time it really makes sense to repair well plugs in a Q-Jet is when doing a numbers matching restoration. (in my opinion)

Just my $.02

[HO455]

As was stated the plugs are to block passages that are left o byver from the machining process. Even GM hasn't perfected the drill bit that can turn a corner. The use of plugs is found in virtually every carburetor. The Quadrajet seems to have a worse reputation from leaking plugs than other carburetors do. (The size of the main well plugs may contribute to the reputation). It is my belief that the whole quadrajunk reputation comes from this issue.
The reason they start to leak has to do with fact the plugs are made of steel and then are peened or crimped in place. The raw casting had extra material around the spot the plug fits into. Then a special machine would crush that extra material down locking the plug in place tightly enough to prevent fuel from leaking past. As the vehicle gets driven the carburetor goes through thousands of heat cycles. The material the plug is made of has a different expansion rate than the pot metal used in the carb body. Thus the plug will over time deform the hole it resides in allowing fuel to flow past. The leakage rate depends on how loose the plug gets. Thus a vehicle that has spent its life in a moderate climate and was never overheated may not have a plug leaking (or it doesn't leak enough to be noticeable if it is a daily driver). But if the vehicle spent time in extreme cold weather and then was severally overheated at some plugs will the plugs have been forced to the deform the casting to a greater extent and greater leakage results.
GM became aware of the problem and came up with the band aid fix. They had hard foam plugs that sit in the base plate and push against the bottom of the plugs installed. This slowed the leakage to an acceptable level to get the vehicle past the warranty period. Plus it only cost pennies per unit and didn't interrupt the manufacturing process.
The expansion rate problem exists for all fixes. In addition epoxy products are generally not fuel resistant and will fail. Having tried dozens of products there is "no cure all miracle product" that fixes the problem once and for all. I will admit to never having tried Belzona as the buy in price is rather high and no guarantee it would seal any better.
Having experienced this problem myself many times know that you can make good repairs that will last for years .
I do have to disagree with the statement that Q-jets made after 67 don't have problems with the well plugs leaking. It simply is not true. The fact that that there are very few 1966 Q-jets out there. There are no where near enough 1966 carburetors to ruin the reputation of the millions of carburetors that followed.

[Greasey Harley]

Originally Posted by HO455

...I do have to disagree with the statement that Q-jets made after 67 don't have problems with the well plugs leaking. It simply is not true. The fact that that there are very few 1966 Q-jets out there. There are no where near enough 1966 carburetors to ruin the reputation of the millions of carburetors that followed.

Yeah, I screwed that statistic up pretty good. I was too lazy to look it up. should have said:

Very early carburetors used pressed-in brass cup plugs in the bottom of the main casting. This process was used through 1968. The leakage rate for these units was almost 100%

Units made after (about) 1968 used pressed in aluminum plugs, a few of them leak, but not nearly as often as the early style brass plugs.

The swaging process was improved in later carbs. It is rare to find a Q-jet manufactured after 1975 with leaking bottom plugs, However they should always be tested.

Source:
How to Rebuild and Modify Rochester Quadrajet Carburetors
by Cliff Ruggles

[Orange Crate]

Here is some rebuild info's for Q-jet might help...

http://vetteworks.tripod.com/qjet.htm