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dch306 fast idle adjustment

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Wondering if i can adjust the fast idle with the car running if i disconnect the auto choke. I have modified the heat shield to give good access to the adj screw under the carb.

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The fast idle is set at the factory and doesn't usually need adjusting.


The fast idle cam (the light color plastic thing above) has steps on it. The more the choke is on the the farther the cam moves to a higher step. The fast idle set screw closes on this step and gives the (more or less) proper idle speed for the choke setting used. When the choke warms the cam progressively steps the idle speed down and finally linkage falls down of it's own weight turning the fast idle cam out of the way of the set screw and the carb is now running on it's normal idle speed.


You can bend the linkage so that when the choke is on, it pushes the fast idle cam farther and onto a higher step.

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I meant to say adjust it with the wire off. Its a rebuilt carb. The idle is fine after it warms up but way too high for the first few minutes.until the auto choke moves. My original carb was fine. One owner car.78 b210. but I like having spares for everything. I was really impressed with the quality of the rebuild. They even  rebushed the primary throttle shaft . Don't know how they ever found an exact replacement. It was that company in Florida. I guess I'll just try to adjust it a bit and see how it goes. I can always take the carb off but its running so good I hate to mess with it. Thanks.

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Fast idle is 1,800 to 2,200 with the choke fully on, on a cold day. This is normal.


Once started just step on the gas and it should idle down some.


The choke may be set too rich.


Hold the throttle open slightly and push the choke open and closed and you'll see what moves the fast idle cam.

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Thanks. Another reason to keep my old carb is for reference without having to take that darn air cleaner off.

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