Carburetor Tech

Seems at some point in recorded history, just about every company from textiles, to baby food manufactured some sort of Carburetor for the internal combustion engine.   Although the manufacturers have been reduced over the years to just a few, the variety is still there in many different models of the same style.
For those Quadrajet freaks, we will gets our paws dirty and jump into one of the hundreds of models of Rochester Quadrajets.

We will start here with model number.  This is found on the right side of the case toward the rear on a flat panel where the secondaries are.  If you can't find it, clean the area with a little carb cleaner and wipe with a rag and you will see it.   Our number is a 7044288 which shows up as a 1974 Quadrajet off of a Chris-Craft Boat with 307 engine and automatic transmission linkage.   Amazing where people find some of these carbs to go on their trucks.   Oh well, once rebuilt it will run pretty much the same as the rest.
The important part here is not so much to identify where it came from, but to get the correct kit to rebuild it.
We were then off to the local Auto Parts store with our model number to buy the correct kit.
Important note:   When you buy your kit, don't tear off the plastic wrap until you are certain all the gaskets and small parts are the same.   If you go ripping into it and it's wrong, you can't return it for the correct one.   Most kits are designed for a multitude of models so you may find 6 sets of gaskets and 50 different small parts, but the main thing to remember is you can identify some of the gaskets by shaking the parts around in the box and verifying that some look the same as the gaskets your going to take off.  Next we will start the dis-assembly process and gain access where we can identify the gaskets and parts are correct.
BTW: When you buy the kit, get a fuel filter too as it's not included.

Here is our grungy carburetor.
Take a good look at this point looking for any missing parts, and rods.


Remove the choke pull off and if accessible place a vacumn pump on the pull-off, pump to 10 to 12 inches of vacumn and see if it holds.  If it does it's good, but if it bleeds off, replace it.

With a small punch (or in this case a nail to show that it can be done) tap out the accelerator pump pin, but stop just before it hits the case.  If you bottom it against the case your going to have a difficult time getting behind it with a screwdriver to push it back in when the time comes.






Now go around the top of the carburetor removing the screws including the two tapered ones inside the primary venturi's.
There will be 2 at the back, 2 at the side, 2 right behind the primaries, 2 inside the primaries, and one at the front.   Some of these screws are different lengths, so make note which screws go in which hole.   While your at it get a small flat blade screwdriver and remove the small screw right between the secondary butterflies and remove the Secondary metering rods and the holder.

Carefully separate the top.   The accelerator pump will more than likely either come off with the top, or the spring will kick it out to one side.   Don't worry about this, just set it aside along with the spring.
Now carefully remove the float, float rod, and needle valve.  If applicable you will also have to remove the bakelite insert that will cover the float.   With that out of the way, carefully pull up on the retainer (a small screwdriver around the edge helps) and remove the primary metering rods and the spring below the metering rod pistion.  It will require turning the carb upside down to remove the spring.   You can save the spring removal step until you remove the accelerator check ball as detailed below.(Editors note:  We had failed to get a picture of this step and plan to add one later, but with care, you will figure out the step without needing a pic.  The exploded diagram that you have with your kit will help).


A turkey pan makes a good parts holder during the rebuild and the used parts left over after the rebuild can be thrown away when you toss the pan.


Carefully remove the main jets, the needle seat (not shown but look at your diagram), and the small screw next to the accelerator pump that holds the check ball.
Carefully turn the carb upside down to drop the ball out of it's bore.  If you saved the removal of the Primary Metering rod spring until now, be careful with this step as the spring is small thus it's wise to have it over your turkey pan so the loose parts will drop in there incase you miss catching them.


If you haven't already done so this is also a good time to remove the fuel inlet nut and the spring and filter.
I hope you bought a new filter while you were at the auto parts store buying the kit.


In the foreground is the two idle mixture screws that need to be removed and placed in your pan.   Don't worry about the setting, as we will get to that on re-assembly.


Two screws on the bottom plate and it can be removed.   Make sure if you haven't removed the accelerator pump bracket to do it now noting it's position for re-assembly since on most models there are two positions for the linkage.







Here is a view of the removed Idle Mixture Screws.

With the bottom plate separated from the main body, make sure you haven't missed removing anything that should not be immersed in carb cleaner or sprayed with carb cleaner which is basically anything plastic.   Remove all easily removable traces of gaskets. The cleaners will remove them and soften them up but if your using the dip method, the gasket material will contaminate the chemical causing it to loose it strength sooner.
The preffered method I use for Carb Cleaning is the "Dip" such as is distributed by Safety Kleen, or Berrymans both of which are somewhat environmental friendly but needs recycled when dirty. These "dips" come in a 5 gallon bucket with a screen bucket to put all your parts in and then dip into the chemical for a couple of hours.  Once all the stuck on stuff is softened up, it can be hosed off with water and if done correctly comes completely clean.
Check all small parts to make sure they are clean and also account for all parts put in the bucket while cleaning.
The other method is cleaning with aerosol type cleaners.   While this method works O.K., it doesn't equal the cleaning power of the Dip.   Using aerosol cleaners requires a good face shield, nitrile gloves and long sleeve shirts.  You don't know pain until you squirt yourself in the eye with carb cleaner (been there) plus it burns skin, takes 2 layers of skin off your hands and removes fingerprints quite effortlessly, and is generally really nasty stuff.   We use Berryman Carb cleaner aerosol to kill wasps that wonder into the shop and it is 10 times better than that over the counter wasp spray that will kill on contact 20 feet away, so use protection if your spraying off your carb.   Again, make sure all parts are clean and accounted for.  Cleanliness is key.

With all parts clean, blow out all passages with compressed air.  The best method for this is blow each passage hole you find and listen for air excaping from another passage somewhere else.  Unless it's a screw hole, you should get air movement through all passages as you move from hole to hole, just beware that some of these holes may contain some amount of carb cleaner and if blown into your eyes or skin (see comments above).


Here we look at the Bottom Plate, Main Body, and Top Plate that are now clean and ready for re-assembly.


Get your kit out, verify that all gaskets and parts look right and let's get ready for re-assembly.

Look at your exploded diagram and get famaliar with the parts and figure out where any parts may go that you are not sure of since the dis-assembly.   If you haven't got your kit yet, you can look at ours for now, but use the one you have for re-assembly and not ours as there are many models and inherent differences between them.
Click on the picture to open a new window and see the exploded view.














We opted to use a new float for this install also.  It's not necessary to replace the float, but is good peace of mind and insurance from not having to break the carb open later and replace it.


One of these things is not like the others.....   With a couple of choices of gaskets in each kit, make sure you have the exact match to your old gasket you took off before putting it in the dip.


Fit the correct gasket to the bottom then place the bottom plate onto the body.  Tighten the screws just hand tight.   Overtightening of these screws will just cause them to strip out ruining the carburetor.


Install the two main Jets, but pay careful attention not to burr the screw slots in those jets.  One burr could cause a disruption of fuel flows and un-desirable results.


Find your accelerator check ball amoungst the packages of parts in the kit.


Install the new check ball and install the screw just a touch over snug.


Install the new neoprene seal on the accelerator pump shaft.


Sometimes dis-assembly is required to install the new seal but most often it requires just removing the old seal and slipping the new one on, allot like putting an o-ring on a shaft.


Install the spring in the accelerator pump bore.


Next install the acclerator pump.


Open the package and install the Needle seat and gasket in the body.   As with Main Jets, be careful not to burr the soft brass while installing the seat assembly.


Using your exploded diagram, install the needle valve and retainer on the float along with the float rod and carefully install the float, making sure the needle valve and retainer stay on the float.


Carefully bottom the float on the needle valve while not lifting the float out of the bore.  Using the measurement laid out in your exploded diagram, adjust the float using the guage provided in the kit.
Our setting called for 1/4 inch.


Here is a view of primary metering rod and spring.


Install the bakelite insert, spring and primary metering rod assembly.   Again, a small screwdriver around the edge of the retainer will seat the metering rod piston retainer, preventing it from coming out.
IMPORTANT NOTE: A little patience will be needed during this step to get the metering rods to fall in the main jets, but with the correct the alignment, they will slip right in.
Do now force the metering rods, and they are very easily bent.


Find the top gasket that matches your old one and install it.
There are cutouts in the gasket so you can fit the gasket without the need to remove the primary metering rods again, just be careful not to rip the gasket during the installation.

Now we are ready to put the top back on, but this little jewel of a Choke Linkage can be a real pain and requires patience to over come.   This is probably the hardest part of the whole assembly.
As you place the top back on, you will need to align the top so the air bleeds line up with their respective holes and that the choke linkage goes into the correct hole, does not fall off, and drops in the right direction so that the choke assembly will line up with notch in the choke linkage.


With everything in position, put a couple of screws in the top to hold it together and move to your choke linkage.


A little shaking, rattling, and rolling, along with finese, and a small screwdriver and the choke linkage will line up as shown.
Install the choke assembly now along with the secondary linkage, and install the screws and tighten.


Here is a look at the assembled choke and secondary linkage assembly on our particular carburetor.


Now install all the screws and tighten hand tight.  The screws inside the primaries are tapered and need to be tight so as not to loosen and fall out, going down the carburetor and into the engine.
Remember though not to overtighten.
While your here, go ahead and carefully install the secondary metering rods.  Again, care needs to be taken to line them up and drop them into the correct holes, and once line up is coorect, the bracket will drop right over the screw hole and allow you to install the small screw and tighten just snug.
This screw will break very easily.


Once the top screws are tight, go back and re-check the bottom ones.
Incase your mounting this on an open plenum manifold, you don't want these screws falling out, but again, do not overtighten.

Install the idle mixture screws until they just start to bottom out, then back off 1 1/2 turns each.
If you are not a sea level, you will need to adjust these once you start the vehicle by turning them in until the idle smooths out and the engine no longer runs rich.  Make sure engine is a operating temperature and then turn one until you hear an increase in idle (smoothing out) then turn the other.
Experience with a vacumn guage is helpful here but with a good ear you can get it close.
Close adjustments for 4000 feet sea level is about 3/4 to 1 turn or less.


Install the accelerator pump linkage and with a small blade screwdriver, carefully pry the pin back through the linkage hole and into the bracket on the opposite side.
This is also a good time to install the Fuel Inlet nut, spring, gasket, and a new fuel filter.  Installation needs to be snug but don't over tighten here as the threads are small and very easilly stripped.


Match your mounting gasket to your old one so you have it when your ready to install your carburetor.


Here is the finished product with all linkages in place, ready to install.   Installation is the reverse of removal so if you remembered how it came off, it should go right back on.
If your not famaliar with tuning or are unsure of the install, find a buddy that has done it, or ask someone with knowledge in mechanics to help you.

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