Re: 75 hp 3 cyl. evinrude
The first thing you should do, is to buy an OEM service manual. Next on the list is to search this site and others for information on rebuilding carburetors.
To answer your basic question, yes you should clean every part of the carburetors. A complete rebuild kit for each carb should be purchased and all of the parts for your carbs (the kit may contain parts for other carbs) should be used. All passages and jets should be cleaned thoroughly and the new floats should be adjusted. The rebuild kits (three) should cost you a little under a hundred dollars.
You will also need a special screwdriver to remove the fixed high speed jets. If you do a search on this forum, you should find a couple of threads on this issue, with one or more describing how to make the necessary screwdriver out of a standard one.