Rebuilt the carb but the seat that the needle valve goes into is much longer than the original I pulled out. Also the needle has a pin that goes into the end that has a spring on it, not like the original. What does this spring do?

This causes the float to be very rigid and does not move easily like in the original set up. Any thoughts? Should I just clean the old? Thanks for any insight.

Oh yeah, Its a carter YF on a 235.