Rivera Primo SU Sportster KIT 1041-0064 - Manual (Page 11)

Guide dome over the piston return spring to compress
it. Dome will fit on body only one way, so insure that bolt
holes in the dome line up exactly to the bolt holes in the
body.
Install piston with piston tube pointing up into the dome.
Be sure to align the piston keyway with the piston guide
located on the carb body.
Install Piston return spring.
Piston fully seated in SU body.
41
40
39
38