Copper tanks were often used on the 1942 or 1946 motors. The usage seems to have been limited to the two-horse Sportsman. I\ve owned three or four of them. After I get them running, I let other people have them.
The only rationale I can suggest for the use of copper was that by 1942 the USA had joined WWII and the use of aluminum in civilian articles was strictly controlled. FWIW, Evinrude didn’t build any outboards for civilian use from early 1942 until 1946 when the war was finally over. The copper tanks on the 1946 Sportsman likely represent leftovers from 1942 that were being used up, after which Evinrude went back to the pressed aluminum tank. The tiller grip should still be rubber over an aluminum handle. Here’s a picture of one of mine running on Lake St. Scratch back in 2005. Hope this helps.
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Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...