I have a b and a c carb for the tohatsu mfs6. it came with the c and it fowled so often I replaced it with a b. over time I lost track of which is which, and they are visually identical. I know the c is ported smaller, which lowers emissions and reliability. I have them both broke down, any hints on how to tell them apart? I want the b on the motor and the c as a spare.