Mercury Black Max 150hp Plugs

I have a 1984 Mercury 150hp Bl

I have a 1984 Mercury 150hp Black Max that runs good at high speed but when idleing out to the no wake zone it shakes and splutters and doesn't run smooth. I use Mercury Quicksilver oil mixed at the correct Ratio. The motor isn't oil injected. It calls for the NKG BU8H ring fire} plugs and that's what I have in it now. When I take them out to check them they are black and have oil on them. It runs better for a while when I clean them then same old thing. What I would like to know is there a hotter plug I can use without doing any damage to the engine?

"Ken, a hotter plug won't

"Ken, a hotter plug won't solve the issue, but perhaps an adjust/sync on the carbs may help. Sounds like you are running a little rich..."

"Thanks, Graham I will try tha

"Thanks, Graham I will try that and it does seem to be running a little rich and not burning all the fuel. The plugs being oily I assume too much fuel and it's not burning it all. Thanks again."

Trouble shooting starts with a

Trouble shooting starts with a compression test!!! Then check that your motor is indeed firing on all 6 cylinders ( use a timing light ) for that or a spark checker each cylinder must fire a gap of 7/16" .Then check if the motor is actually warming up. Some people have a bad habit of removing thermostats and that will cause bad idle / fouling.

There is no other plug for tha

There is no other plug for that motor. Than is it running rich. Check the fuel pump diaphram. And the carb jets are not always the same size. They go to a certian cylinder.