Notice that my exhaust tip have darken after out on long cruises. I remember back in day my then 55 exhaust tip showing a light blue gray after trips. Now on the 272- 2bl-3spd OD, same setup as then show black. Which tells me it might be burning rich. Should I look in to this with that in mined? Some had suggested it might be from the modern fuel. I use pump regular fuel. Only thing I believe mileage is not that good, appear to be running good. Rebuilt carb, without a change. Any suggestions are welcome.