Maybe your air/fuel screw is way out of line? I think stock is 2 1/2 turns out. Yout definetly getting to much fuel by the way you
described your plug. The stock jet on the Big Bear is a 112.5

 

When I put the carb back together the third or fourth time, I reset the air/fuel mixture screw to the correct setting. I think it was 2 1/2 turns like you said, but would have to look it up to be sure. I got the number from a member on here.

My question is, if I want to adjust the mixture to get less fuel, which way would I move the screw? Would it be out or in?

Maybe I can adjust the mixture a little more to make it right.

Thanks.