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3-screw SU vs. 4-screw SU

BTF/PTM
BTF/PTM
in Carburetor Central

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Posted
comment_314688

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.

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https://www.classiczcars.com/forums/topic/35308-3-screw-su-vs-4-screw-su/
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comment_314763

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

comment_314781

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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