I've looked through the carby forum and the Z-Therapy site and can't seem to find the answer to this question. Is there any difference in performance between the three screw and four screw carbies, I know that one was used on early Z's and the other on late ones but I'm not sure about the performance issue.

I have a three screw set on my project 260 and a spare four screw set that the previous owner of the 260. I would like to know so I can choose which to hold on to and which I should sell on.

Not much in the way of performance difference if any between the 3 and 4 screw SU's. The 4 screw usually are the preferred choice in that they hold the damper housing in better alignment.

I guess it's a matter of personal choice and which carbs are in the best shape that you have.....