If you haven’t done so already, pull the cylinder head and check the vertical water passage at the back of the head. When I rebuilt my CD-11 I found this passage partially blocked with trash/debris. I’ve had a couple other motors where this passage was also clogged, on one motor it was totally blocked with leafy, weedy material. See pic.
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."