spark plugs?

I have a 1989 Evinrude E120TLCEM, the local mechanics replaced the Champion QL77JC4 plugs with NGK R BPZHS 10 plugs, it appears I've carbon fouled the plugs? I've been having a lot of issues with the boat running good for about 20min and then when I go to an area of the lake where I've got to idle, when I try to go back out and hammer down the motor has no power? I've been told it could be the coil packs, so I ordered new ones. But after reading some posts, I'm just wondering if the idling is the problem, but I don't know how I can avoid that, around all docks it's always idle speed. The other issues is when motor is at idle getting a lot of smoke? Seems to me to be running really rich? Other boats on lake don't appear to be spewing smoke like mine? Even at low speed I can see a light haze behind boat. I'm new to this boating thing so don't know what things should be

Thanks for the help