I typically wet sand my final coat of primer with 600 and then 1000 grit before applying the color coats. Note that any imperfections that show in the primer will also show up in the color coat, so getting the primer really smooth is critical. 120 grit is pretty coarse – if you use that to get rid of old paint and rough spots in the metal, then I would follow up with 400 and then 600 grit before applying primer. Here’s a pic of one of my cowls after 3 coats of primer and wet sanding before applying the color coats. I suppose everyone has a slightly different approach but this is what works for me.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
1982 Evinrude 25hp
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."