Article 956 - Engine Stall or Hesitation on Acceleration

TSB #52 - December 2, 1966
(Supplement to Article No. 932 of November 4, 1966)
(1967 Units with 4300 Design carburetor Built Prior to Approximately January 3, 1967 - 289-4V, 390-4V NON-GT, 428-4V)

Occasional customer complaints of engine stall or hesitation on acceleration may not be fully resolved by the accelerator linkage modifications outlined in previous Technical Service Bulletin, Article Number 932 of November 4, 1966. Recent investigations indicate a check valve replacement or a change in accelerator pump stroke adjustment may also be required to obtain complete customer satisfaction. The following diagnosis and corrective procedure should be used if the referenced accelerator pump modification kit does not provide adequate problem correction.
    1. Remove the air cleaner assembly.
    2. Observing through the air horn, look for fuel spray from the pump vent when the throttle is quickly opened and closed a number of times (10-12). Refer to Illus. S1148-A and S1149-A.
Wetting, seepage or small fuel droplets emanating from the vent is considered normal. If the valve is seating normally, change the pump pivot pin to the number three hole (right hand hole) and readjust the vent valve to specifications (.070 inch). If fuel spray is observed at the check valve, a new rubber valve (Part No. C7AZ-9576-B, Class B) is required to correct the problem. The plastic valve contained in tune up and gasket kits, should be discarded and replaced with the new rubber valve for service installations. The following is the service procedure for replacing the valve:
    1. Remove the choke clean air pickup hose from the carburetor.
    2. Remove the fuel inlet hose from the fuel filter.
    3. Remove the pump rod to pump lever assist spring and washer from the pump rod.
    4. Remove the choke control rod to automatic choke lever "E" retainer.
    5. Remove the air cleaner anchor stud and the air horn to main body retaining screws (eleven screws).
    6. Carefully lift the air horn from the main body. Allow the air horn retaining screws to drop into a dish or tray by inverting air horn.
    7. Lay the inverted air horn on a bench or table. Remove the pump valve retainer and plastic valve (see Illus. S1150-A).
    8. Insert the new rubber valve into the valve cavity and install the retainer. NOTE: The cross slots in the retainer must face the valve and the base of the retainer should be flush with the casting surface (see Illus. SI 149-A).
    9. Carefully position the air horn assembly over the main body and guide the pump plunger and air valve piston into their respective chambers, while lowering the air horn on the main body.
    10. Install the air horn to main body retaining screws. Install the air cleaner anchor stud.
    11. Insert the choke control rod into the automatic choke lever and install the "E" retainer.
    12. Insert the pump rod into the pump lever. Position the flat washer on the pump rod and install the pump assist spring.
    13. Install the fuel inlet hose to the fuel filter and the choke clean air pickup hose to the air horn.
    14. Install the air cleaner assembly. Carburetors with date code 6LC and later incorporate this new accelerator pump rubber check valve.

Illus. S1148-A &
Illus. S1149-A
Illus. S1150-A

Oper: 9631-A
Time: 0.5 hrs.