HESITATION 3/4 - FULL THROTTLE REPLACE DIST./CARB.-NEW P/N'S

SOME 1985 AND 1986 TRUCKS MAY EXHIBIT A HESITATION WHEN THE ACCELERATOR PEDAL IS APPLIED 3/4 TO FULL THROTTLE, AT LOW SPEEDS, IN GEAR. THIS CONDITION IS CAUSED BY INADEQUATE SPARK ADVANCE AND A LEAN AIR-FUEL MIXTURE AT LOWER ENGINE RPM. THE VEHICLES INVOLVED WERE BUILT DURING THE ENTIRE 1985 MODEL YEAR AND UNTIL JANUARY 1, 1986 OF THE 1986 MODEL YEAR. TO REPAIR THIS CONDITION, REPLACE THE DISTRIBUTOR MAIN SHAFT ASSEMBLY P/N 1977695, WITH MAIN SHAFT ASSEMBLY, P/N 1978266, AND REPLACE THE CARBURETOR, P/N 15501852 WITH CARBURETOR, P/N 15553355. CUT THE VACUUM HOSE TO THE DISTRIBUTOR VACUUM ADVANCE CAN AND INSERT A VACUUM ADVANCE DELAY VALVE, P/N 14020691, INTO THE CUT HOSE, WITH THE BLACK SIDE TOWARD THE VACUUM SOURCE. ADJUST THE INITIAL TIMING FROM 10 DEGREES BTDC TO 8 DEGREES BTDC. THIS UPDATES THE ENGINE TO THE LATEST 1986 CONFIGURATION. USE APPLICABLE LABOR OPERATION NUMBER AND LABOR TIME.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.