How much oil do you mix with a 35 horse Johnson boat motor?

I'm sorry, but you need to know the year of manufacture. If it's post-1968, 50/1 is OK. If it's pre-1958 or so, use 16/1. In between, Johnson/Evinrude went to 24/1 for a few years, then 50/1, and I don't know the exact year they went to 50/1. I would research that and make sure you are using the mix they suggested for the year of your outboard.