EXPERTEC TSB (57-2)

WARNING: This page is about the Spectrum Base, 2D Hatchback, Automatic, which is a different variant/trim than selected.

Publication date: 1984-06-27
Reference number: 57-2

EXPERTEC TSB

TECHNICAL SERVICE BULLETIN

Reference Number(s): 57-2, Date of Issue: 06/27/84

CARBURETOR VACUUM BREAK - TEST PROCEDURE

Model(s): All GM Models

Bulletin No.: Chevrolet 57-2

Pontiac 84-6(GAS)-53A

Oldsmobile 84-T-24

Buick 84-6C-12A

Cadillac T85-97

GMC 85-B-64

Date: 06/27/1984

BULLETIN ILLUSTRATION LIST

Fig 1: Graphic

Fig 2: Graphic

SERVICE INFORMATION

HARD STARTING OR POOR WARM-UP PERFORMANCE ON A CARBURETED ENGINE MAY BE DUE TO A LEAKING VACUUM BREAK UNIT. THE VACUUM BREAK, SOMETIMES CALLED THE "CHOKE PULL-OFF", OPENS THE CARBURETOR CHOKE VALVE AGAINST THE TENSION OF THE THERMOSTATIC CHOKE COIL DURING COLD ENGINE START-UP. A VACUUM BREAK UNIT WITH A LEAKING DIAPHRAGM WILL NOT OPEN THE CHOKE VALVE TO THE PROPER POSITION, AND MAY CAUSE A COLD ENGINE TO LOAD UP WITH FUEL, RESULTING IN BLACK EXHAUST SMOKE. VACUUM BREAK TESTING PROCEDURE:

SERVICE PROCEDURE

DETERMINE WHETHER THE VACUUM BREAK HAS A BLEED ORIFICE. IF IT DOES, IT SHOULD BE PLUGGED AS SHOWN. SEE Fig 1 FOR POSSIBLE LOCATIONS. MOST REAR OR SECONDARY SIDE UNITS HAVE A BLEED. MOST FRONT OR PRIMARY SIDE UNITS DO NOT.
USE HAND-HELD VACUUM PUMP TO APPLY 15" HG (51KPA) VACUUM TO THE VACUUM BREAK, (Fig 2 ).
- A. THE VACUUM BREAK PLUNGER SHOULD MOVE FULL TRAVEL. APPLY FINGER PRESSURE TO PLUNGER TO SEE THAT IT HAS MOVED THROUGH FULL TRAVEL. IF NOT, REPLACE THE VACUUM BREAK AND ADJUST TO SPECIFICATIONS. THE LABOR OPERATION TIME FOR REPLACING THE VACUUN BREAK UNIT INCLUDES ADJUSTMENT.
- B. THE VACUUM BREAK DIAPHRAGM SHOULD HOLD VACUUM FOR AT LEAST TWENTY SECONDS. IF IT DOES NOT, REPLACE THE VACUUM BREAK AND ADJUST TO SPECIFICATIONS.

REMINDER, THE CARBURETOR VACUUM BREAK IS COVERED UNDER THE FIVE-YEAR 50,000 MILE EMISSION CONTROL SYSTEMS WARRENTY. REFER TO THE "DIVISION" SERVICE POLICIES AND PROCEDURES MANUAL.