How to Adjust the Automatic Choke on an Aircooled Volkswagen (VW) Beetle

Reviewed by Jason Shackelford

Last Updated: December 10, 2024 Approved

The automatic choke regulates the air/fuel mixture during engine start up. It produces a richer fuel/air mixture when the engine is cold, then gradually makes the fuel mixture leaner as the engine warms up. This is accomplished by a butterfly valve in the throat of the carburetor, at the very top. When this valve is closed the flow of air is very much reduced and the fuel/air mixture is rich. When the valve is open the flow of air is maximized and the fuel/air mixture should be correct for a warm engine..

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Find the automatic choke.
- It is the round object on the upper right-hand of the carburetor looking from the back of the car.
- There is a wire coming to it from the positive side of the coil. Check this with a trouble light for voltage when the key is on.
- The choke is held in position by a triangular ring clamp and three screws so it can be loosened and rotated for adjustment.
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Pull the throttle arm on the left side of the carburetor down to free the cam (little step arm) that the screw at the top of the throttle lever rests on.^{[2]
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- With the engine cold, the butterfly valve should be closed.
- As the engine warms up, the coil voltage heats an element inside the automatic choke, causing a bi-metal spring to uncoil, opening the butterfly valve, and moves the cam to reduce the idle speed.
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Release the throttle arm so that the return spring snaps it back.^{[3]
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- When cold, the little screw at the top of the throttle arm should now rest on the top step of the stepped cam.
- This sets the hi-idle, which is needed together with the choke on a cold engine to provide sufficient idle speed to keep the engine running until it warms up fully.
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Keep your eye on the butterfly valve in the carburetor throat.^{[5]
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- Turn the choke element clockwise until the butterfly is standing straight up. Then turn the choke counterclockwise until the choke butterfly fully closes (not too tight).
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Start the engine with the air cleaner off.
- As the engine warms up, make sure that the butterfly opens until it is standing fully open when the engine is fully warm.
- If it doesn't fully open,put your finger briefly on the ceramic of the automatic choke and see if it is hot. If not- you need a new one. Try it again in the morning and see if it opens enough to drive it. Check that it is wide open when warm. Re-adjust until you get it right.

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What should I do if the vehicle won't turn on again after I turn it off, and the butterfly stays open?

Jkchd07

Community Answer

Check your battery connection first. If there isn't a good ground connection, it won't come on.

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