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3-screw SU vs. 4-screw SU

BTF/PTM
in Carburetor Central

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What's the difference? My '72 currently has 3-screw SU's on its L28, and the second engine I have (F54/P90) has 4-screw SU's on it. Oh, and I'm referring to the number of screws holding the domes in place.

How about this one?

The dealership replaced my flat tops with new round tops in 1980. After learning what these carbs are, I noticed mine has a 4 screw for the front and a 3 screw for the back. They work fine, just odd.

Bonzi Lon

S
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Their isn't much difference from what I heard about the 3 or the 4 screw carbs, other than the screw patterns. I don't know but I'd bet you could use the pistons in the dash-pots interchangeably and a lot of other parts, I bet Bruce would know if that was the case.

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