Throttle Body

Remove accelerator pump rod from throttle lever.
NOTE: It is not necessary to disassemble throttle body any further. Do not remove idle mixture screw plugs unless it is necessary to replace mixture screws or cleaning and air pressure fails to clean idle mixture passages. If necessary to remove, proceed as follows:
Invert throttle body and position on a holding fixture with manifold side up. Position a punch in between 2 locator points on manifold side of throttle body. There are 2 locator points adjacent to each mixture screw.

Fig 1: Exploded View of Rochester Model M4MC 4-Barrel Carburetor
Courtesy of GENERAL MOTORS COMPANY
Using a hammer, drive punch against throttle body to break out portion of throttle body to gain access to idle mixture screw plugs. Drive out hardened steel plugs.
NOTE: Hardened steel plugs will shatter. It is not necessary to remove plug completely. Remove just enough pieces to allow idle mixture adjusting tool (J-28706) or a thin walled 3/16" deep socket to be used to remove mixture screws and spring.