Figured out why I couldn't get it to idle right

[Banditorama]

I guess I missed it when I cleaned the carb out the first time

Why would someone do this to the idle mixture screw?

It's. 030 shorter than it's supposed to be, so someone intentionally reworked the shape for some reason. It's way sharper than it's supposed to be and the taper on it is uneven as well.

[Marshall V. Daut]

There are lots of different sizes and length idle mixture screws out there. Often they were designed for carbs other than Model A, such as for tractors or smaller CFM carbs. Because they are "close" and the threads fit, these idle mixture screws have been tossed into Model A carburetor "rebuild" kits for years. Sometimes, they almost work. More often, though, if they can't be reworked and reshaped, they get tossed. Or worse, the Model A owner leaves the improper idle mixture screw in place and bitches about poor performance and mileage. The shorter screw tip in your photo looks too good to have been modified in someone's garage on a bandsander. My guess is that it was made this way and was considered "close enough for a Ford" and slapped into your carb. Not all Model A vendors sell rebuild kits with the right parts. Caveat emptor.
Marshall

[mercman from oz]

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Banditorama figured out why he couldn't get it to idle right