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 5/16" Primary Throttle Shaft

Carburetor Bushing Kit #4301


 Installation kit will eliminate worn and leaking primary throttle shafts on all year Rochester Quadrajet carburetors. 


If your not familiar with all of the carburetor components and their placement, it is advisable to take digital pictures of the carburetor, linkages and springs to help you re-assemble the carburetor.  Installing bushings in a Quadrajet is a simple job, but care must be taken to drill straight, following the existing bore centerline.  The enclosed specially machined drill bit is piloted  to aid in alignment.   If you have any questions, call us at (908) 362-7692. 

1. Remove carburetor from engine and drain all gas into a proper container.

2.    Remove base plate from carburetor :

Remove 2 long air horn screws located on the top/rear of the carburetor behind the secondary air flaps.  Remove 2 or 3 Philips head screws from the underside of the base plate.   Gently separate base plate from body casting.   Disconnect accelerator pump linkage rod, freeing base plate completely from carburetor.   Apply penetrating oil to throttle screw threads.

3.    Place baseplate  in a soft jawed vise:

With primary bores facing up and  primary throttle blades open fully.  Carefully secure the base plate in the soft jawed vise, so throttle blades remain fully open.

4.    Using a small metal file, carefully file off the 4 protruding throttle blade screw threads flush with the shaft:

 This step is required so the screws will not strip the threads on the throttle shaft.   Take your time and do not mar the ID of the base plate throttle bores.

5.    Remove 4 throttle blade screws:

Remove base plate from vise.   Mark each primary throttle blade, so that it can be returned in the same position & location, later on.   Use a sharp/square screwdriver and carefully remove the screws completely.

6.    Remove secondary throttle return spring:

Take note of how the 2 secondary springs are positioned for later re-assembly.   Twist external secondary tang to pre-load the spring, allowing the outer secondary spring to be removed.   Slid external secondary linkage off shaft and remove rod from primary shaft.

7.    Remove primary throttle shaft:

Ensure that there are no burrs on the throttle shaft and carefully remove shaft from housing.   Be careful not to bend shaft.   Carefully clean primary throttle shaft.

8.    Install base plate in soft jawed vise:

DO NOT attempt to hold the base plate by hand when drilling!

9.    Install drill stop collar on drill:

Adjust collar approximately .550” back from drill cutting edge.  Tighten drill stop collar and double check your measurements.  This will allow the 1/2” (.500”) bushing to sit slightly below the base plate casting edge.  Also by not drilling thru the throttle shaft bore completely, a step will be left to provide a positive stop for the bushing, preventing the possibility of driving the bushing in too far.

10.   Drill out base plate:

Insert drill pilot in primary throttle shaft bore until the pilot is located in the center throttle shaft bore.  The pilot will align the drill,  But it is important that you drill straight in line with the throttle bore center line.  Drill steadily until the drill stop collar makes contact with base plate.  Do this on both outer primary shaft bores.  Bushings are ONLY installed in the two outer shaft bores, not the center bores.

11.   Install 2 bushings:

Verify that both bored holes are at least 1/2” deep before installing bushing.   Apply a thin coating of  Red Loctite #271 threadlocker to the outside of the bronze bushing.   Use supplied installation tool to drive bushing squarely into drilled hole.   Ensure that thread locking compound is not on the ID of the bushing.  Wipe off any excess thread locking compound.   Allow base plate to stand for 6 hours before continuing.

12.   Reinstall primary throttle shaft:

Check for smooth operation of throttle shaft.  The shaft should fit snug in bushings, but should not be binding.   Double check that there is no thread locking compound on throttle shaft.

13.   Reinstall primary throttle blades:

Replace throttle blades in their original locations.   Apply thread locking compound to new screws.   Install 4 screws, but do not tighten.   Ensure that both primary throttle plates are centered in primary bores, open and close primary throttle shaft to “seat” throttle blades..   Snug up screws and double check that throttle blades are still centered.   Carefully tighten 4 screws and check throttle blade alignment once again.  Reinstall secondary springs and linkage.

  14.   Reinstall baseplate.