How does the carter choke work
Senior User
Joined: Dec 2013
Posts: 348
Likes: 4
From: Bakersfield,CA
Have four YFA carburetors and all are different.
One of which is the same as your carburetor with the so called feedback servo air mixture valve on the side that is controlled by the ECU.
When applying 12 VDC from an automotive type to the thermostat choke actuator, the bimetal thermostat coil will move counter clockwise when facing the open coil about 90 degrees from cold to fully hot.
Have one thermostat chole actuator that is open and fails to heat up.
Might want to check your thermostat to make sure it works.
So, when the theromstat cap is installed on the carburetor the coils move clockwise when viewed from the outside surface. The choke shaft must also move clockwise to the open the choke butterfly valve plate from the initial cold condition.
Install the thermostat cap so the electrical lug is at the 12 o'clock position, so the end of the coil is positioned on the left side of the choke shaft tab. The turn the thermostat cap clockwise, so the electrical lug is at 4 o'clock position.
The flat side of the coil will contact the tab on the choke shaft.
Look at the end of the coil and see the wear mark from the tab.
There is a cut on the edge of the cap. Align the cut with the middle notch on the carburetor housing for the initial setting. This is the normal setting.
The required setting of the thermostat is a function of ambient temperature and elevation. With the electrical lug at the 4 o'clock position or the cap set at the normal setting, the butterfly valve will just start to open.
In warmer low elevation climate rotate the cap clockwise from the normal setting.
In colder higher elevation climate rotate the cap counter clockwise from the normal setting.
One of which is the same as your carburetor with the so called feedback servo air mixture valve on the side that is controlled by the ECU.
When applying 12 VDC from an automotive type to the thermostat choke actuator, the bimetal thermostat coil will move counter clockwise when facing the open coil about 90 degrees from cold to fully hot.
Have one thermostat chole actuator that is open and fails to heat up.
Might want to check your thermostat to make sure it works.
So, when the theromstat cap is installed on the carburetor the coils move clockwise when viewed from the outside surface. The choke shaft must also move clockwise to the open the choke butterfly valve plate from the initial cold condition.
Install the thermostat cap so the electrical lug is at the 12 o'clock position, so the end of the coil is positioned on the left side of the choke shaft tab. The turn the thermostat cap clockwise, so the electrical lug is at 4 o'clock position.
The flat side of the coil will contact the tab on the choke shaft.
Look at the end of the coil and see the wear mark from the tab.
There is a cut on the edge of the cap. Align the cut with the middle notch on the carburetor housing for the initial setting. This is the normal setting.
The required setting of the thermostat is a function of ambient temperature and elevation. With the electrical lug at the 4 o'clock position or the cap set at the normal setting, the butterfly valve will just start to open.
In warmer low elevation climate rotate the cap clockwise from the normal setting.
In colder higher elevation climate rotate the cap counter clockwise from the normal setting.
Thread Starter
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Senior User
Joined: Dec 2009
Posts: 139
Likes: 3
Have four YFA carburetors and all are different.
One of which is the same as your carburetor with the so called feedback servo air mixture valve on the side that is controlled by the ECU.
When applying 12 VDC from a lead acid battery or AGM battery to the thermostat choke actuator the bimetal thermostat coil will move counter clockwise when facing the open coil about 90 degrees from cold to fully hot.
Have one thermostat chole actuator that is open and fails to heat up.
Might want to check your thermostat to make sure it works.
So when the theromstat cap is installed on the carburetorthe coils move clockwise when viewed from the outside surface. The choke shaft must also move clockwise to the open the chocke butterfly valve plate from the intial cold condition.
Install the thermostat cap so the electrical lug is at the 12 o'clock position so the end of the coil is position on the left side of the choke shaft tab. The turn the thermostat cap clockwise, so the electrical lug is at 4 o'clock position.
The flat side of the coil will contact the tab on the choke shaft.
Look at the end of the coil and see the wear mark from the tab.
There is a cut on the edge of the cap. Align the cut with the middle notch on the carburetor housing for the intial setting. This is the normal setting.
The required setting of the thermostat is a function of ambient temperature and elevation. With the electrical lug at the 4 o'clock position or the cap set at the normal setting the butterfly valve will just start to open.
In warmer low elevation climate rotate the cap clockwise from the normal setting.
In colder higher elevation climate rotate the cap counter clockwise from the normal setting.
One of which is the same as your carburetor with the so called feedback servo air mixture valve on the side that is controlled by the ECU.
When applying 12 VDC from a lead acid battery or AGM battery to the thermostat choke actuator the bimetal thermostat coil will move counter clockwise when facing the open coil about 90 degrees from cold to fully hot.
Have one thermostat chole actuator that is open and fails to heat up.
Might want to check your thermostat to make sure it works.
So when the theromstat cap is installed on the carburetorthe coils move clockwise when viewed from the outside surface. The choke shaft must also move clockwise to the open the chocke butterfly valve plate from the intial cold condition.
Install the thermostat cap so the electrical lug is at the 12 o'clock position so the end of the coil is position on the left side of the choke shaft tab. The turn the thermostat cap clockwise, so the electrical lug is at 4 o'clock position.
The flat side of the coil will contact the tab on the choke shaft.
Look at the end of the coil and see the wear mark from the tab.
There is a cut on the edge of the cap. Align the cut with the middle notch on the carburetor housing for the intial setting. This is the normal setting.
The required setting of the thermostat is a function of ambient temperature and elevation. With the electrical lug at the 4 o'clock position or the cap set at the normal setting the butterfly valve will just start to open.
In warmer low elevation climate rotate the cap clockwise from the normal setting.
In colder higher elevation climate rotate the cap counter clockwise from the normal setting.
Thank you so much. I appreciate it. I was thinking I had to bend the tab on the choke thermostat coil like a circle and install the shaft in the middle of it. I'm going to pick up a new choke this week. If I have more questions I may message you. I really appreciate your time and help.
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