Ok, my 15 HP Evinrude sat in my yard for 2 years without being used. I couldn't start her. Well, I fixed the carb and she was running. I decided to burn off the little gas that was left (that was also 2 years old) and freshen with a new mix. But, after two years, I couldn't remember what kind of oil I was to use. I ended up putting SAE 30 in the gas mix at the correct ratio. When I took the boat out (first time in two years) she wouldn't full throttle and stalled a lot. Then, I could barely bring her back in on low idle. Someone has told me that I should never put SAE 30 in my 2 stroke engine. Have I already damaged my engine? Is there hope? What should I do to fix this?