From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Service Bulletin for the Stromberg 'AA-25' Carburetor for 1937 Cadillac models.
| Identifier | ExFiles\Box 122\2\ scan0251 | |
| Date | 1st November 1936 | |
| CADILLAC 37-60, 65, 70, 75, 1937 Page 4 STROMBERG CARBURETOR SERVICE BULLETIN CHOKE PARTIALLY OPEN—ENGINE FIRING—FAST IDLE As the engine begins to fire and a manifold vacuum is created, vacuum piston “B” is pulled down to the position where the upper side hole in the piston is exposed to air taken through passage “E”, stopping the pull on the piston. With this action the choke valve opens slightly to admit sufficient air for running. The air flowing through passage “E” draws fuel from passage “F” for the fast idle mixture. ENGINE WARM—SLOW IDLE The choke valve in the carburetor being off center continues to open by the force of the inrushing air, which works against the tension of the thermostat until the thermostat absorbs sufficient heat so that it will not offer any resistance. As the choke valve “A” opens, it allows the vacuum piston “B” to lower until the piston closes passage “E” cutting off the supply of air and gas used for fast idle. Fuel is then only taken through the regular idle discharge holes “N”. ADJUSTING THERMOSTAT 1. Remove thermostat case “G”, allowing thermostat “D” to cool or warm until it has reached the temperature of 70°. THIS IS VERY IMPORTANT. 2. When the thermostat reaches 70°, the inside of hook “H” of the thermostat should coincide with the “zero” marking on the thermostat case, which is the original setting made at the factory. When installing a new thermostat or other new parts, check the zero location very carefully at 70° temperature and change the location if necessary. If it is impossible for the thermostat to reach 70°, you can provide for the difference by allowing one graduation on thermostat case for every 5° variation in temperature of the thermostat. 3. To adjust thermostat, reassemble case onto the air horn so that hook “H” comes into contact with pin on the lever without any tension and with choke valve “A” in wide open position. The zero marking on the case will then coincide with the notch on the air horn. 4. Revolve thermostat case fifteen notches rich as indicated by the arrow and fasten screws securely. BENDIX PRODUCTS CORPORATION STROMBERG CARBURETOR DIVISION SERVICE BULLETIN STROMBERG “AA{D. Abbot-Anderson}-25” CARBURETOR GENERAL DESCRIPTION The Stromberg Model “AA{D. Abbot-Anderson}-25” used on Series 37-60, 65, 70, 75 is a duplex downdraft type especially adapted to the 1937 Cadillac cars. The principle of operation is the plain tube using air-bled jet to maintain the proper mixture throughout the entire range. The carburetor is of aircrait design. The fuel chamber completely surrounds the entire body; this feature enables the fuel to be maintained at the proper level under varying operating conditions. Another feature in the float chamber design are the baffles which help to control surging of the fuel on sharp, sudden turns. The float needle valve is hooked to the float lever which makes it positive acting at all times. A removable plug for checking the position of the fuel level is provided in the float chamber. These models are really two carburetors built into one. There is a set of venturi tubes, a main metering jet, an idle system with an adjustable needle, throttle valve, and a pump discharge nozzle for each barrel. Both barrels are supplied fuel by one float chamber. There is only one air inlet. The idling system supplies all the fuel at idling speeds and also on part throttle up to approximately 22 M.P.H. From approximately 22 M.P.H. to 75 M.P.H. part throttle, all of the fuel is supplied through the main metering system. The additional fuel necessary for speeds above 75 M.P.H. and on all wide open throttle operation is supplied through the economizer valve. An accelerating pump is connected directly to the throttle, this together with the economizer assures proper operation under all conditions. MAIN METERING SYSTEM Fuel enters the carburetor at gasoline inlet through the float needle valve (19) and (20) and into the float bowl where it is maintained at constant level by floats (15). See illustrations. Air enters the carburetor through the air inlet and places suction on the main discharge jet (2) or idle discharge holes (9) depending on the amount of throttle opening. The main metering jets (6) are of the fixed type. They control the flow of gas during the intermediate or part throttle position up to approximately 75 M.P.H. From the metering jet the fuel passes into the main discharge jet (2) where it is mixed with air from high speed bleeder (3) and flows into the carburetor barrel down to the intake manifold. All jets of the fixed type are calibrated at the factory to supply the correct mixture for normal operating conditions and should not be changed without special instructions from the factory. NOTE: A new type of main metering jet is used in this carburetor. To distinguish it from jets of similar design a groove has been added on the shank of the jet. The part number is P-22660 and should not be interchanged with other jets. T-24924 Wrench is used for assembling of jet. IDLE METERING AND ADJUSTMENT Fuel for idle speeds is taken through the idle tube (5) where it is mixed with air from the air bleeder (4). The mixture passes to the idle channel and is then discharged through idle holes (9). On “curb idle” or closed throttle, fuel is drawn only from the lower idle discharge hole due to the high suction at this point. As the throttle is opened, suction is also placed on the upper idle discharge hole to feed additional fuel until the throttle is opened to the position where the main discharge jet comes into operation. When adjusting the idle needle valves, have the engine well warmed up so that the intake manifold is warm to the hand. The idle speed of the engine should be set at a speed equivalent to 7 to 8 M.P.H. by adjusting stop screw (40). The idle needle valves (8) control the fuel for low speed adjustment. Turning OUT the needle gives a richer mixture and turning IN a leaner mixture. Taking one barrel at a time, turn the idle adjustment IN slowly until the engine begins to “lag” or run irregular, then slowly turn OUT until the engine begins to “roll”. Finally, very slowly, turn in the adjustment again, just enough so that the engine runs smoothly for this throttle opening on the mixture to one set of four cylinders. Do the same with the other idle needle valve. It may be necessary, after making adjustments, to cut down the engine speed slightly. [Diagram Legend] 1. Choke Valve. 2. Main Discharge Jet. 3. High Speed Air Bleeder. 4. Idle Air Bleeder. 5. Idle Tube. 6. Main Metering Jet. 7. Main Discharge Jet Plug. 8. Idle Needle Valve. 9. Idle Discharge Holes. 10. Throttle Valve. 11. Automatic Choke Piston. 12. Vacuum Piston Link. 13. Primary Venturi. 14. Auxiliary Venturi. 1937 CADILLAC Models 37-60, 65, 70, 75 STROMBERG CARBURETOR Model AA{D. Abbot-Anderson}-25 No. A-18352 Cadillac No. 1419627 401 BENDIX DRIVE Form 10-136 BENDIX PRODUCTS CORPORATION STROMBERG CARBURETOR DIVISION (Service Stations All Over the World) SOUTH BEND, IND., U.S.A. 11-36-5M-SPI Printed in United States of America. | ||