ROCHESTER CARBURETORS

Bulletin 9D-31  3-10-55

tmpAC-1.jpg
United Motors Service
DIVISION OF GENERAL MOTORS CORPORATION
Bulletin 9 D-31
Date:          3-10-55
Page                     1
Supersedes 9 D-31 Dated 11-1-49
GENERAL OFFICESóDETROIT
ROCHESTER PRODUCTS
CARBURETOR BULLETIN
SUBJECT--CADILLAC
Reported Service Complaints on 1955 Model Carburetor.
1.     Border line lean condition at speeds of 20-40 miles per hour. Consistent operational hesitancy of the engine takes place in this instance throughout the above speed ranges. Engine lacks solid feel.
2.     Stumble on light acceleration. This condition can be corrected by replacing with the new type No. 7000208 Pump Plunger Assembly and the No. 7000204 Power Piston Assembly.
Note: The No. 7000208 Pump Plunger and No. 7000204 Power Piston are now in production.
3.     Stumble and shudder upon light acceleration. It was found that improper ad­justment of idle - i.e, air adjustment screw turned out as far as 9 turns. Idle adjustment screw turned out excessively to balance large volume of air. This brought about an excessively rich idle mixture which created so heavy a draft on the fuel in the carburetor inner well that on light acceleration the distance of fuel left in the main well tubes was increased to a point sufficient to cause light part throttle leanness.
This situation brought about Item 3 above - stumble and shudder. Correct adjustment of the Idle Mixture eliminates the stumble and shudder characteristics,
The lean condition between 20 and 40 miles per hour can be corrected by installing No. 7008768 Primary Cluster in the No. 7007970 and No. 7007971. Production carburetors equipped with this new cluster will carry XB tags, February 1955. Latest specifications Idle Tube . 031, Idle Re­striction .057. Venturi Cluster No. 7008770 for carburetor No. 7007240 Standard Front Eldorado and No. 7007942 Standard Rear Eldorado, also No. 7007241 Rear Air Conditioned Eldorado.
The above corrections need be made only when customer complaints indicate poor performance in the above mentioned instances. It is suggested that thorough inspection of the engine, ignition system, ignition timing and possible accessory manifold air leaks be carefully checked before any attempt is made to make changes in present carburetors.
Policy: This modification is to be handled on a maintenance basis.
(0466 PD 3-55)                                                   - 0 -                                        (Printed in U.S.A.)
AA.GO:9, WD, 131, 132:9-13

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