The top view with the choke open shows how dirty this carb is. Remove the two screws down inside the choke opening, down in the primary barrels. The screwdriver shows the location on one side. These are tapered head screws and help align the air horn, so keep track of them. Directly under the thumbnail in the picture, you can see a small screw attached to the end of the choke plate shaft. Remove the screw and lever it holds to the shaft. Free it from the linkage going down inside the carb. Now remove all of the remaining screws from the air horn (top) and lift it straight up. Don?t force anything. There are several parts that can be damaged if not careful.
Now the top is off of our Q-Jet. Still very dirty and not a good sight. You can see the old gasket on the top of the carb body. You may have several different selections of gaskets in the rebuild kit. If you select the wrong one, the carb won?t work right. You may want to match up the new gasket to the old one before going on. The old one should come off in one piece. Should. Don?t count on it. And save as much of the old gasket as you can in case you lose track of which new one to use.
There is a slit that can be seen where the rod drops through the gasket. This actually continues all the way to the other rod. These rods are the primary metering rods, and like the secondary rods they are available in different sizes. These will have some affect on idle fuel mixture, but will make a big difference as soon as the throttle is opened. The Y shaped lever they are connected to is attached to the enrichment piston. When there is high engine vacuum under the piston it is pulled down, and the rods are dropped into the jets, restricting fuel. When the throttle is opened and vacuum drops, a spring raises the piston and rods. They lift out of the jets and richen up the fuel mixture.
With the gasket off, you can see the accelerator pump. There is now nothing holding the accelerator pump, and it will lift right out. Note the spring under the pump. It can be seen in the carb, under the pump. Lift the spring out of the carb at this time.
The top of this rod is the one the accelerator lever pushed down. When the rod is pushed the spring pressed the cup seal at the bottom of the assembly and forces fuel into the primaries for acceleration enrichment. This supplies a shot of fuel to overcome the sudden rush of air when the throttle is opened. Then the metering rods take over.
The small plastic collar at the top of the enrichment piston hold the piston and primary metering rods in place. Gently use a small screwdriver and lift the assembly out of the carb body. Be very careful not to bend the unit. Any bends will change the fuel mixtures at all points of operation. And it will likely change mixture side to side. Be careful. With the piston out, you will see a spring under the piston. Remove it as well. Notice that there is another spring that puts tension on the metering rods, and is attached to the piston linkage. Pay close attention to how it is mounted.
You can see the position of both the accelerator pump spring and the enrichment piston spring in this picture. The part being removed holds the float pivot in place. It is a plastic piece. Doesn?t look like much, but the carb will flood without it.
The float pivot is the arced shape piece. Directly in between the pivot and the enrichment piston bore you can see a small pin in its own bore. Do not remove or turn this unless necessary. It is the adjustment for the minimum primary rod position. Changing it will change the fuel mixture at low engine speeds and idle. If you are building a performance engine, you may want to change it a bit. Otherwise, leave it where it is. Turning it down will lean the mixture, raising it will richen the mixture.
If you feel you must remove this adjustment, count the number of turn required to bottom it, the remove it. When reinstalling, bottom it then turn it back out the same number of turns to return it to its original location.
This tube just lifts from the carb body. It does, well, nothing. It just displaces some fuel space. Earlier versions don?t have this, or the space for it in the carb body. Computer control versions use this space for the connection to the mixture control solenoid. Keep in mind this is a 1975 carb, and electronics did not come into regular production until 1981.
This space is used for an accelerator pump restrictor in some trucks with EST systems. The restrictor allowed a full shot of fuel from the accelerator pump when the engine was cold. Once warmed up it restricted accelerator pump quantity. This was done to make the EPA happy. It often made the truck hesitate on acceleration. If you are not dealing with emissions, just leave it disconnected. Where emissions are important keep it connected.
Under the screwdriver in the photo is the float. It?s the black fiber piece down in the float bowl. The float bowl is the opening in the body where fuel is stored and level maintained. Again you can see the arced float pivot. You can see it is turns under itself and provided the pivot for the float. Note the metal section of the float itself under the arc. You can also see a very small spring in front of the arc. This is the top of the needle valve spring. It is also hooked on the metal part of the float. Being behind the pivot, when the float raised, this section drops, and vice verse. It raises or drops the needle valve into the seat to allow fuel into the carb, or stop it. The whole thing is not unlike a toilet tank valve.
Grab the arc pivot, and lift it out of the body. You will get the float, and needle valve with it. The small boss on the top of the needle is where the needle spring clips, and holds it to the float. The brass seat can be seen below the needle.
Now the brass seat can be seen very easily. Note the notches for a screwdriver. It requires a large screwdriver to remove it. A small one will just touch one of the notches, and cause the seat to be damage. On removal we don?t really care. We will replace it with a new one. Damage to the new one can cause fuel starvation or flooding.
Just under the screwdriver is a retaining plug. It is a plug with a pin attached to the bottom. The pin restricts a check ball located under the plug. This ball is the accelerator pump check ball. You will have new one in the rebuild kit.
MAN WHAT A MESS. There should not be any of this dirt and crud build up in the carb. This is one of the nastiest ones I have seen. That what happens after 29 years on the car and 5 years of sitting.
Although it?s hard to see through the muck, the screwdriver is now pointing at the primary metering jet. On the other side of the enrichment piston bore is the other one. These are where the primary rods drop in to control fuel flow. The jets are marked with a number. The larger the number the larger the jet. Larger jets will increase fuel flow at all stages of primary carb operation. So larger jets richen the primary operation. Smaller jets will make it leaner. Usually, jets are changed instead of metering rods to adjust fuel supply.
Remove the accelerator pump plug, check ball, seat, and primary jets.
Here are the primary jets, accelerator pump check ball and check ball plug or retainer.
Now flip the carb upside down. There are 3 screws holding the bottom plate, the throttle plate, to the carb body. Remove the screws and separate the throttle plate from the body.
Once again, pay attention to the gasket position. Remove the gasket.
These are some of the soft plugs in the Q-Jet. Remember we are looking at the bottom of the carb body. These are noted for leakage. When they leak, fuel will drain from the float bowl when the car is shut off. The result is a long cranking time when restarted. The fuel pump needs to fill the carb back up before it will start.
Some carb kits have a foam like piece that gets place at the bottom of these plugs to seal them. If your carb has been rebuilt before it may be there. Don?t worry if you kit does not have one. After cleaning, and epoxy can be applied to the bottom of these plugs to seal them forever. JB Weld works well.
The very black area is where the PCV valve flows through the carb to the intake. When restricted the PCV system won?t operate properly. You may have good vacuum but low flow.
The idle adjustment screw can be seen at the left. It is the screw with the tension spring on it. The spring provides tension and keeps the screw from turning on it own. Leave it alone for now.
Here is the fuel filter. You may have removed it when taking the carb off of the car. If not take it out now before cleaning. Watch for the spring behind the filter.
The black disc is the choke coil cover. This one is a bit rough, but functional. It can be rotated clockwise to make the choke open sooner. Rotating it counter clockwise will make the choke stay on longer during warm up.
Vacuum pulls hot air up from a heat tube in the intake manifold, through the housing, and heats the coil. Newer versions have electric heating coils. These can easily be spotted by a single electrical connector on the cover. There is only one wire for the heater. The ground is through the housing.
Most covers are held in with rivets. If yours has screws it has likely been adjusted or replaced before. Drill off the heads of the rivets. Be careful of the retainers under the rivet heads. Retainers spinning on a drill bit can create damage. Once the heads are off the cover can be removed. Use a punch and drive the remaining parts of the rivets out through the back of the choke coil housing.