Carter YF & YFA Choke System

Testing your choke

With the engine off and the engine cold.
Press on the accelerator a bit to allow the choke to close.
Look down the carburetor throat to make sure the choke valve is closed (most of the way).
Start the engine and let it warm up.
Turn the engine off and look down the throat again. You may have to press on the accelerator again a bit to allow the choke to open.
The choke valve should be completely open now.
Electric Choke
Test the voltage coming to the thermostat hot wire (with the key on). It should be close to 12v.


YFA Choke System
Carter YFA Choke Fast Idle Cam

When the choke is closed, engine cold, the fast idle cam will be positioned so that the idle screw is sitting on the high step. Adjust the fast idle using the Idle screw.

YFA chokeThe choke housing contains the choke pull down piston. The piston is controlled by vacuum. When the engine is cold and you step on the gas, this pull down piston opens the choke valve slightly so that the engine doesn’t choke out due to lack of air.

If the piston is frozen remove the aluminum plug at the bottom of the piston well and tap the piston out with a brass drift punch. Clean so that the piston will move freely. These pistons are not available so be careful not to break the lever, or stem.

YFA Choke RodThe hot air connection is used to connect the hot air tube. Vacuum supplied to the choke housing pulls the hot air into the choke housing. This heats up the choke thermostat, which then will open up the choke valve.


The choke rod connects the fast idle cam to the choke shaft and is used to move the fast idle cam.

Watch a video about the YFA Choke:

Updated on 04/13/2022

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