Classic cars repair

Old Carburetors

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This model is standard equipment on the Superior Chevrolet Series "K and V" cars. It is a multiple jet, plain tube type of carburetor with only one adjustment, which is for idling or low speed.
Principle of Operation
The jets in base of multiple jet nozzle feed gasoline to carburetor well and nozzle chamber.
A combination of gasoline and air is drawn into nozzle chamber through the jets on side of nozzle, forming a fine spray which is carried by the stand pipe to venturi, or main air passage, where it is absorbed by incoming air forming mixture on which engine operates.
Jets on side of nozzle come into operation in direct proportion to throttle position. The further the throttle is opened, the more jets are in operation. At wide open throttle all jets are working and engine is getting maximum supply.
Maximum economy is obtained at 20 miles per hour and minimum at wide open throttle.
Low-speed jet assembly supplies gasoline to engine at idle engine speed and up to approximately 15 miles per hour, gasoline flowing through a drilled passage connecting low speed jet chamber with carburetor well.
At idle, gasoline is drawn through low speed jet and idling port at edge of throttle valve.
Idle adjustment screw regulates amount of air entering this port. Backing out adjusting screw admits more air and consequently makes idling mixture leaner.
Dirt may sometimes get into the jets and cause engine to run unevenly or to spit and back fire.
This dirt may often be drawn out through jets by closing choker and opening throttle wide when car is running 25 to 30 miles per hour. Hold choker closed about 2 seconds, then open choker, also open and close throttle until engine fires evenly.
If dirt cannot be removed in this way, carburetor should be taken apart and cleaned (see also next page).
If it should become necessary to remove jets, make certain that proper size screwdriver is used so as not to destroy slot. In view of the fact that jets are made of brass great care should be taken when cleaning not to increase size of drilled holes which regulate amount of gas supplied engine. When replacing jets, care must be taken that they are screwed in tight against their seats so that gasoline passes through proper drilled holes and not around the threads.
A choke valve is provided for use in starting and warming up engine. This valve is operated by a knob on instrument board.
To start, turn on switch, open throttle slightly, and press starter pedal. At the same time, pull choker knob clear out, pushing it back part way as soon as engine fires. It should then be pushed in gradually as engine warms up until, when thoroughly warm, knob is in as far as possible.
Adjustment of Carter "RXO"
As previously stated, model "RXO" has but one single adjustment which is the low-speed, or idling adjustment.
Idling adjustment: Refer to Fig. 1, and set the idle adjustment screw from one to one and one-half turns from its closed position, at which point the engine should run evenly without loading or missing.
If not, and further adjustment is necessary, turning the idle adjustment screw to the right or clock-wise will give a richer mixture, and, turning this screw counter-clockwise or to the left will give a leaner mixture.
The idling speed of the engine is regulated by the throttle lever adjusting screw shown in Fig. 1.
This screw acts as a stop for the throttle lever and prevents the throttle valve from closing too tight, thus causing the engine to stop when the accelerator is released.

NEEDLE SEAT GASOLINE INTAKE NEEDLE/ FLOAT LEVER LIP FLOAT LEVER PIN FLOAT BOWL Fig. 1. Internal views of the Carter model "RXO" carburetor with one adjustment for lower idling speed (no high-speed adjustment).

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Carburetor Manuals: Carter RX0