Quadrajet carb rebuild

Rat Rods Rule

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Well-known member
Sep 26, 2009
Winnipeg, Canada
Some may not like Qjets, but I've had good luck with them.

This is an old set of notes by Dorian Yeager. These notes are tried and true and I've used them for 6 or 7 rebuilds.

Locate choke rod. Passenger side of carb, attached to the choke blade.
Older ones will have rod connected to choke blade shaft
with either a clip or (early ones) or the linkage from the rod to choke shaft
will be screwed on with a flat blade screw (later models). Remove clip or
screw, or linkage. (later) Leave the choke rod as it is...just note that to remove and install the upper 3rd of
the carb casting (the "air horn") the choke rod needs to fit through the gap
there...it tends to move during reassembly, and block downward movement of the air horn.
Now, on to the accelerator pump lever. Green lever
on drivers side of carb, front, top. See where it pivots on the roll pin?
That pin needs to be pushed "in". Get a suitable punch.
I've even used a small Allen wrench, tapping the end of it with a
hammer..much easier with suitable punch though. Use small taps, just enough
to move it slightly each time. You MUST not push it through so far that it
hits the carb body. Leave just enough space between casting and roll pin that a screwdriver blade can be used to push pin back through during reassembly. As you are pushing
pin through, periodically wiggle accelerator rod..., wiggling eventually will free it, before pin is all the way through. Now you can remove accelerator lever, but leave the rod that attaches lever to primary throttle shaft connected..no reason to remove it. Next, remove the one small flathead screw on the secondary hangar and remove the secondary hangar/rods by pulling it straight up. Be careful with the rods, they are quite soft. if they are gummed up, clean them off..if corroded, use VERY fine steel wool (0000) lightly to remove corrosion..they are only plated with chrome, over brass. Remove all 9 flathead screws holding air horn to the float bowl. (center section of carb)
Looking down on top of carb: one up front, two INSIDE the primary throttle
bore (push choke butterfly open) Two behind primary bore (remove metal shield with screws if so equipped) Two screws on either side of the air valves, and the two at the rear, behind the air valves.
Air horn should lift off, if with a little force. If necessary, a little prying force with screwdriver on the passenger side, between choke housing and air valve will break them free. It doesn't take much pressure..if it does, you've done something wrong. Once it's broken free, lift it straight up..notice (on most models) four brass tubes pressed into underside of air horn. Don't bend them. Accelerator pump (what the accelerator pump lever pushes down on) may try to come out at same time.
Now you will be looking at the floatplastic spacer, and power piston. Accelerator pump just lifts out. Notice rubber seal on one end. You will likely be replacing the steel rod, and that seal. Removal of the springs and pump cup SHOULD be included in the kit instructions, and is pretty self explanatory anyway. The spring in the pump bore is not easily removable, as far as I can tell. Next, remove the plastic spacer in the float bowl. It is odd shaped,
usually flat on top. Will lift straight out. Underneath the spacer, you can
see where the float pivots. On some carbs, you will have to remove the power piston first. Its the kind of "t" shaped piece that is sticking above the
level of everything else in the float bowl, almost in the center..you should
be able to depress it slightly with finger pressure, and it should spring
back up. If gentle lifting pressure doesn't free it, try depressing it, then
letting your finger off quickly, letting spring force it out of its bore..may
take a few times...The rods attached to the Power Piston are the primary metering rods, again, if corroded, say from sitting long periods of time, buff them with 0000 steel wool or equivalent. Remove the spring that is likely still in the PP bore.
There is a relatively thick shiny "clip" that the float pivots on. About
1"/1.5" long. Pull it straight up. Note what comes out with it, and how the
needle is connected to the float. Should be replacement needle and clip in
the rebuild kit. The needle seat is the brass slotted piece which it pulled
out of. Large flathead will allow you to remove that, and the seat should
also be included in the kit.
No need to remove the primary jets (at bottom of float bowl, what the end of the primary rods go into) which are brass, unless the carb, again, is very corroded. They require a thick flatblade screwdriver to remove. Also, near the accelerator pump, you will notice a single flat blade screw. Remove that, and under the screw, sometimes stuck, is a check ball.
Use a Q-tip to clean out the area the check ball sits in, and replace ball and the screw.
Once all that stuff has been removed, turn carb over. Later models (after '75) will have a plastic "cup" on the passenger side of the carb that
will fall out. Just remember to install it. On the bottom of the carb, remove
2 screws. That will separate the float bowl from the throttle body (bottom, 3rd casting) now you are all set to clean. My favorite implements to clean are: Toothbrush, dental pick, sharp screwdriver paint thinner, and pan large
enough to hold carb castings over to clean.
Remove the idle mixture screws. Front two screws with springs on front of
the lower casting. Clean all passageways very good.
PCV port usually carboned up. Blow air through the idle mixture
screw ports.
So now everything is clean and dry. Attach throttle body to float bowl
with the two screws, not forgetting the gasket. (will not be a super thin
gasket, nor the thickest. Thickest gasket is of course carb to intake. Medium
thickest gasket goes here. Make sure the accelerator pump rod, if still
attached, doesn't get pinched when assembling these two halves. Torque screws down hand tight...too much and they will strip, just like valve cover bolts.
Now to reassemble everything in float bowl. Grab float, assemble the
needle and clip, and the float pivot pin. The needle clip hangs off of the
rear of the float "arm", but NOT through one of the holes...it balances on
the flat section in the center, and mates up to the seat. (brass piece with
four slots) With pivot pin through float "arm", and needle hanging off back
of float, lower the assemble down, making sure needle mates up to the seat,
and doesn't slip off the float. Pivot Pin should bottom out.
Depending on carb, the plastic spacer will likely have to go on now, over
the float/pivot pin. Now the hard part. The power piston, with the metering
rods, needs to go back into it's bore. Install the spring first, then put the
PP over top of it. Should slide over the spring. be careful here...the rod
tips need to mate up into the jets on both sides, so the PP can down all the
way. The tips are soft..no force here, just trial and error until they line
up. Once you get them mated up, press the plastic disc on the PP down into
the bore evenly..it retains the PP from popping out very easily. The PP
should move freely up and down with finger pressure.
After refurbishing the accelerator pump per the kit instructions, install
it in it's bore..the rubber seal goes in first, so it's near the bottom of
the bore. The spring will force it up, so you have to watch that as your
mating the castings up.
Select correct gasket for the air horn to float bowl , as there will
likely be at least two different ones. The easiest way to do it is install
the gasket UNDER the top of the PP hangar (the "t") first without ripping the
gasket. the gasket needs to go completely underneath the hangar. Watch the choke lever, as it needs to fit through the gasket also. Align gasket on the two dowels, and push the accelerator pump down, and slip gasket over the top of it, mating up the correct hole with the top of the accelerator pump. Spring pressure on the accelerator pump will force the gasket up, and the PP too.
I hold the gasket down near the Accelerator pump, so it can't force it
up. Mate the 4 tubes in the air horn up to the float bowl, the choke lever
through the air horn, and the accelerator pump through the air horn. Once
they are all mated up, air horn should mate up to air valve with very little
clearance. If it doesn't, something isn't seated all the way, likely the PP.
If it mates up close, install the screws for the air horn. Now go through and
connect the choke rod to the choke, and the accelerator linkage to the
accelerator lever, and the accelerator lever to the air horn with the roll
Some points to consider...don't mess with the choke adjustment. Don't mess with measuring linkage angles and such as suggested by the manual, unless you are certain someone has bent them. DO NOT remove the butterflies on the air valve, choke or throttle body. The screws are weak, and are spread by the factory on the end to prevent
loosening. They will break and you will have to get another Q-jet throttle
shaft, unless you feel like grinding the ends off first.
Idle mixture screws for reassembly? I turn them all the way in (snug)
then back them off 4 turns each. Then unscrew or tighten each one until idle
gets worse, rather than better, then back off until best idle. Do each side
one at a time, will need to work back and forth to get smooth idle. Good time
to check timing.
I'm sure I missed something, so if I did, let me know. It REALLY isn't
this hard, just hard to write it..but I've done it enough times..just take
your time and don't force anything.

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