Can someone help me identify what part this is? Its a mikuni 42 of a 2001 fxdx.

 

You have a Mikuni HSR42 Carb conversion that fits 1991 - 2005 Dyna's among other Harley's. See the link below for more photos and they have a pdf of the carb manual.

https://www.jpcycles.com/product/400...carburetor-kit