Carter UT Catalog
Carter UT Updraft Carburetor Manual


UT Idle Circuit
Carter UT Idle Circuit
Carter UT Float Circuit

Carter UT Float Circuit

Fuel for the idle low speed is drawn from the float bowl A and goes through passage B, past the main jet adjustment C, up the channel and through the idle jet D. The fuel is mixed with air from passage E and then travels through the economizer jet F. Part of the air fuel mixture enters the carburetor bore through port G and the balance travels past the idle mixture screw and into the bore at H.

 

The idle mixture is controlled by turning the screw clockwise to lean the mixture and counter-clockwise to richen the mixture.

If adjusting the idle mixture screw doesn't seem to make a difference, then you have something wrong with your carburetor. Could be dirt, or possibly a vacuum leak. Be sure you are adjusting at idle speed, or it will not work.


Do not try to remove the jets E & F. They are permanent.

Adjusting the Idle Mixture
  • Warm up the engine
  • Adjust the idle speed to specification
  • Turn the screw out a turn
  • Turn the screw in 1/4 turn at a time, waiting a second to let the engine catch up.
  • When the RPM starts to drop, turn the screw back out 1/4 turn.
High Speed Circuit
Carter UT High Speed

Fuel is fed to the carburetor through the main metering jet C.

As the throttle valve is opened (higher speed), the velocity of air going through the bore creates a suction at the main discharge. This causes fuel to enter through the main jet C and mixes with air through jet K. The fuel air mixture travels through nozzle L and into the carburetor bore.


Adjusting M clockwise will leans the mixture. Counter clockwise will richen the mixture.
About 3 turns of the metering screw should get optimal speed.
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