Getting Started with your Rochester
Quadrajet Overhaul
The steps in a Rochester Quadrajet overhaul are: disassembly, inspection,
cleaning, modification and repairing defects, reassembly and adjustment.
In this instruction manual the modification
and repairing of the baseplate throttle shaft defect will be covered in
full detail, along with the correct techniques on how to successfully
install the bushing kit to insure maximum performance.
As shown below the only tools you will need
are a drill press, a 25/64 drill bit, and the 5/16 guide shaft provided in
the bushing kit. The easy out that is shown is only needed should you want
to remove a bushing once it is installed. You will also need the standard
tools that all mechanics have on hand such as a hammer, pliers, etc.
Bushing Kit Service Procedure
Oil, dirt, varnish deposits, water and gum
deposits are some of the main causes of poor carburetor operation. Proper
cleaning is essential when installing the bushing kit.
Once you have soaked the throttle body base
plate in good carburetor cleaner and rinse thoroughly, (high pressure
water is the best way to rinse) blow out all passages in casting with
compressed air. Do not pass drills through passages. Use proper safety
precautions whenever air or water pressure is used.
Disassembly of Throttle Shaft
Experienced technicians develop their own
order or method of disassembly. It is probably best for a beginner to
follow the methods in this manual very closely. The most important tool or
asset of any carburetor repairman is a keen sense of observation.
Before disassembling the base plate, place the base plate on a suitable
stand or legs. We prefer to put a pry bar in a vise where the base plate
will be at eye level.
Now install one of the rear mounting holes
in the base plate on the pry bar where the base plate sets somewhat level
and near your eye level.
The first step in removing the primary
throttle shaft is to bend the primary lever that holds the secondary
actuating rod about 45 degrees as shown in the picture below. This will
allow the rod to slip off later when you're ready to remove the throttle
shaft. By bending this lever now before you remove the throttle plates you
insure that you won't bend the throttle shaft by accident. When the
throttle plates are removed the throttle shaft bends very easy so you will
need to be careful.
The next step will be to remove the four
throttle plate screws. The most reliable method for doing this is to turn
the screws in and break them off. The factory screws break very easy, then
turn the base plate over and with either needle nose pliers or a small
needle point vise grip pliers unscrew the screws from the bottom. There is
always enough screw exposed from the bottom side to catch a hold of where
you can easily remove the screws.
If for some reason there isn't enough screw on the bottom side to catch a
hold of then the next step will be to turn the base plate upside down and
grind the ends of the throttle plate screws enough where they are not
mushroomed enough to cause the screw not to travel back through the
threads. Any small grinder with a small stone should work, however you
must be careful not to accidentally grind any other part of the carburetor
except the screw ends.
Should you break a screw while trying to
back it out then you must drill the screw out and retap the threads. The
stock screw size is 3-48, should the threads become enlarged, then you
must tap to the next larger size and install a larger screw. In this event
contact us and we will send you the larger tap and screws. However, this
can all be avoided by simply turning the screws in and breaking them off
and removing them from the bottom as previously described.
Remove the screw, spring, and the fast idle
adjusting levers from the right side of the base plate and keep in mind
their proper order. Now remove the throttle shaft. When the throttle shaft
is about one inch out of the base plate the secondary actuating rod should
begin to come off, however you may still need to use needle nose pliers to
help separate the lever on the rod.
Once the throttle shaft is out inspect it
for deep grooves. If the shaft just shows signs of normal wear then take
wet 400 sandpaper and sand the shaft where the wear is until those areas
are very smooth.
Drilling Base Plate and Installing
Bushings
Install base plate in drill press vise with
guide shaft as shown in the picture below. Tighten drill press vise with
guide shaft as shown in the picture above. Tighten drill press chuck to
assure alignment, then loosen chuck and remove guide shaft and install
25/64th drill bit. The base plate should now be aligned with the drill
press.
Begin drilling the base plate slowly, and
only drill as deep as the length of the bushing. You only get one chance
so be sure not to drill too deep, and drill with only one stroke so you
don't make the hole too wide. Now drill the other side the same way.
On the late model Q-Jets the right side is
very thin so you will need to drill very straight so that the base plate
won't crack later when you install the bushing on that side. However, if
the base plate does crack, contact us and we will send you a longer
bushing that will correct that problem.
Remove base plate from vise, and hold it in
one hand while tapping the bushings in with the other hand with a brass
hammer. The bushings should pound in without too much effort, but tight
enough where they don't need loctite. Even though the bushings once
installed can't go anywhere, they may need some form of loctite if they
appear loose enough where you can move them with you finger.
Now you're ready to re-install the throttle
shaft in the base plate. When the shaft is about two inches out begin to
install the secondary actuating rod on to the shaft while installing the
shaft.
Once the shaft is all the way in the base plate make sure that the shaft
turns freely, if it is too tight then remove the shaft and inspect for a
tight spot. Usually in this rare occasion you may need to slightly ream
the right side of the base plate housing, but not the bushing, with reamer
or hone. Start with the reamer size .310 to .312. If the shaft is just a
little tight but moves freely where your return spring will still return
properly that's acceptable and will loosen more during normal operation.
Install one throttle plate aligning the
holes as close to center as possible. Turn the shaft and make sure that
the plate seats correctly and there is a very little light showing when
you hold the base plate up to a light. Use the screws that are included in
the kit. Now install the second throttle plate the same way, it should
follow suit with the first plate. When both plates are installed correctly
there should be very little light showing and the shaft should turn
freely. Tighten screws tight but don't break them. Turn the base plate
over and with a small ball peen hammer slightly tap on the bottom of the
screws while positioning the screws head on a punch or the pry-bar. A
slight tap is all that's necessary to insure that the screw can't loosen
and wind up in the engine. Now turn the base plate right side up and
re-tighten the screws again.
With needle nose pliers straighten up the
lever holding the actuating rod to its original position and install the
screw, spring and fast idle levers to their original position.
Now inspect the base plate for normal
operation. The primary throttle shaft should turn without too much effort
and engage the secondary throttle shaft correctly, the primary throttle
plates should close correctly with very little light seen, and the fast
idle lever's should spring back and work correctly.
Satisfactory performance of the Q-Jet can
be obtained once all the defects have been repaired, this bushing kit will
eliminate one of them which causes a great deal of the poor idling, and
running response conditions.
Purchasers of this product may
install (or use) it. However, we highly recommend that in
appropriate cases the purchaser engages the service of a professional that
has experience with the product.
Article
reprinted with permission of Barker
Gang Garage
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