3.3L HPDI plugs?

Did Yamaha change the plugs in the 3.3L HPDI motors from BKR7EKU to BKR6EKU? Did the older 3.3L engines use the 7s and the newer motors use the hotter 6s? Or did they have a problem with the 7s fouling so they went to a hotter plug?

I noticed a miss in my 225, and found that the top starboard plug was really sooty. I am hoping it is just the plug, and not something else.



Thanks

[boats.net]

The 2003 and newer VZ225 uses BKR6EKU plugs.

Sesfoam

At the first sign of soot it's time to use Seafoam. 1oz per gallon will help keep your carbs and cylinders clean and prevent ring seize.

I installed new plugs and ran the motor today for 30 min. The top starboard plug did the same thing, it was covered in black soot after just 30 min of run time. What could be causing this?