Saturday, February 15, 2020

Resealing Quadrajet Well Plugs | Part 1

My '76 Corvette starts and runs fine when the engine is cold, but once it reaches operating temperature and I stop somewhere for 15 or 20 minutes, restarting takes more than a few cranks and, once it starts, it runs rough for 30 seconds or longer.

Everyone I spoke to about the issue said it was due to leaking carburetor well plugs.

Was it the primary or the secondary well plugs? More than likely the former but why take chances?

If the carburetor was to come off of the engine, then might as well bite the bullet and tear it apart, then reseal all of them.

Easy enough, right?

No. Not really.

In my opinion, Quadrajets are a miracle of engineering and, consequently, have lots of components that usually are interconnected to something else through a network of oddly-shaped rods and levers.

So before you start removing this and that and the other, you want to educate yourself, as much as possible, on the process of disassembling and then reassembling a Rochester Quadrajet carburetor.

There are hundreds of YouTube videos on the subject, but most are useless or at least confusing. The few worth watching, in my opinion, are the ones published by Harold Demes and Classic GBody Garage.

Another great video, although not as detailed as the previous ones mentioned, is How to Rebuild a Carburetor: Quadrajet 4 Barrel by Power Nation.

Once you've got a pretty good idea as far as how involved the process is as well as a basic understanding of how to proceed, then you can start taking your Quadrajet carburetor apart.



I let the carb sit on the bench for a good hour, and then looked underneath since you can see the primary wells without taking the carb apart. They were covered in gas.


The first thing I did was give it a good cleaning. You won't be able to get into every nook and cranny, but the first wash will give you easier access to the many screws that have to be removed as well as a clear view of how parts fit both on the carb as well as with other components.


Mine was not super dirty but still was in need of a bath. There are many cleaners available, but some tend to be too caustic. I like to use Gumout Carburetor & Parts Cleaner.

With the carb somewhat clean on the outside, the dismantling began.

The first thing I removed was the air-cleaner assembly stud. This part is easy to remove and reinstall, in case you get cold feet about taking off other components.


I then removed the vacuum diaphragm after taking lots of photos with my phone to have a visual record of how components fit together. Trust me, you cannot shoot too many photos or videos.


The photo below shows how I had to push the hose off of the vacuum nipple with a flat screwdriver. Time, heat, and other factors have a tendency to glue hoses to metal. Fortunately, this hose can be reused.


Here's the choke vacuum diaphragm. I left the actuating rod in place to make reassembly easier. I also like to keep any related hardware with the part, hence the two screws.


I also checked the diaphragm to ensure it was holding a vacuum. All you have to do is push the actuator arm in, hold it, then plug the end of the hose with your fingertip and release the arm.

If the diaphragm is doing its job, the arm will remain in and release when you remove your fingertip off of the hose.

Next, was the electric choke. First, I painted the black (and hard-to-see) dot with a silver marker. This indicates the position of the cover in relation to the locator markings on the edge of the case.

I then removed the cover in order to gain access to the single screw that secures the electric choke assembly to the carburetor body.



The red arrow below points to the screw that secures the base of the electric choke to the carburetor body.


Once the assembly is off, I loosely put it back together to keep all the parts in place. Again, this helps quite a bit during reassembly.



Moving to the other side of the carburetor, the next part that needs to come off is the accelerator pump lever and actuating rod (red arrow).


You will need a pretty thin punch or something else that could be used as such, in order to remove the rolled pin that secures the accelerator pump lever to the air horn (see red arrow above). I used a 3/32" punch (photo below).


Basically, you want to push the pin back enough so you can remove the lever. Needless to say, don't hit it too hard. If you break the tab, you're... well, SOL!



This is the accelerator pump lever and actuating rod. Again, I keep the parts together to make my life easier during reassembly. Make sure to notice how the rod is attached to the throttle mechanism and take plenty of photos.


Also, notice how the pin is out of the way but not far enough to touch the body. You will need a little bit of clearance in order to be able to push it back into position during reassembly.


Back on the choke-side of the carburetor body, you can remove the secondary lockout lever. Guard it with your life as they are very hard to find.


You also want to remove the fuel filter since every component, as well as all fuel and air passages, need to be cleaned thoroughly. This is also a good opportunity to replace the fuel filter during reassembly.


Next, remove the screw that secures the secondary metering rod hanger and remove the hanger and rods off of the carburetor by gently lifting them up.


Next, remove all the airhorn screws that secure it to the body.


Depending on the condition of the gasket, you may have to use a putty knife to separate the air horn from the carburetor body. Just take your time and, for now, leave the gasket attached to the body.


If you are doing a full carburetor rebuild, you want to use the old gaskets as a template to ensure you use the correct ones on your Quadrajet, as rebuild kits usually come with several different gaskets that fit other similar carbs.


Carefully lift the gasket and take out the accelerator pump and spring.


You can now (carefully) remove the old gasket. This can be especially tricky around the primary metering rods hanger. The gasket has slits that allow it to seal that area, so take your time.

A small flathead screwdriver may come in handy to lift parts of the gasket so it comes out in one piece.




With the gasket off, you can now remove the primary metering rods along with the hanger, power piston, and spring.

Also, remove the plastic float bowl insert (red arrow below) and the cavity plastic insert to its left.


With the plastic float bowl insert off you can now lift and remove the float by pulling up the float hinge pin.


Notice that my float does not have the needle hanger wire clip. The carburetor operates fine without it, but this is totally optional. I think it is better and safer to forgo the clip instead of installing it wrong, something that is not uncommon.


One word of caution. The photograph below shows the power piston adjustment valve (red arrow). DO NOT mess with it.

Its function is to regulate the depth of the power piston, which in turn determines how far down into the jets the primary metering rods go, so leave it alone unless you have a darn good reason not to.


Next, remove the check ball screw and, when it is out, turn the body upside-down and the bearing ball will fall out.


At this point, you can leave the carb upside-down and loosen the two baseplate screws (red arrows below). Some Quadrajet carburetors have three.


With the screws and lock washers removed, you can separate the baseplate from the body assembly.

As the photo below shows, not all of the rods and levers have to be removed in order to take the carburetor apart, unless there's a specific need to. But for resealing well plugs, this is as far as you need to go.


I created a PDF list of all of the disassembly steps detailed here. You can download it or print it if you think it would be helpful. However, this list is applicable to my Quadrajet. Yours may be slightly (or significantly) different.
I know that I always obsess about cleaning things, and this time is no different. So I cleaned the carburetor's air horn, the body, and the base plate to the best of my ability. I also sprayed carb cleaner in every orifice I could find and I may do that once more before I put it all back together.

And I also cleaned and polished a few of the parts below. I even chased the threads of the air cleaner assembly stud.


Cleaning the metering rods allowed me to determine their size. The primary rods are 49K (as far as I can tell), while the secondaries are CH rods.

By the way, some of these Quadrajet metering rods are no longer available so used parts are the only viable alternative. Of course, you always take your chances when buying used parts, especially something as delicate as metering rods, so if yours look good, just clean them and reuse them.



In the meantime, I ordered a few replacement parts, including new size 77 jets, from QuadrajetParts.com.

By the way, when ordering replacement parts from a specialist, have your carburetor number ready so you get the correct parts.


So this is the end of Part One of this project, and the only thing related to my carburetor well plugs is that I scraped off most of the old Epoxy.

In Part Two, I will show you how I resealed all the plugs which, hopefully, will take care of the hot-engine hard-starting issue, so stay tuned. (That's what I tell my Quadrajet carb - LOL).

Thank you for following my 76 Vette Blog!



Product Links... (#sponsored)

Gumout Carb and Choke Cleaner | Spray 16 oz.
J-B Weld Dark Grey TankWeld Gas Tank Repair
Rochester Carburetors by Doug Roe
How to Rebuild & Modify Rochester Quadrajet Carburetors by Cliff Ruggles

ACDelco Carburetor Repair Kit: Ball, Clips, Gaskets, Screws, and Seals


1975-1985 Rochester Quadrajet Hot-Air Choke Remanufactured Carburetor


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