3-screw SU vs. 4-screw SU

[BTF/PTM]

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.

[Bruce Palmer]

3 screw carbs and manifolds has provision for water into the carb body for extra preheat.

[Bonzi Lon]

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

[ajmcforester]

My 4 screws have water heating

[Diseazd]

Maybe Bruce "screwed up"!

[Bruce Palmer]

Maybe Bruce "screwed up"!

Now, cut that out!! nyuck nyuck......

[ajmcforester]

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.