Spark Plug Question(s)
 

I've got twin Yamaha 200hp OSX series outboards on new boat. One engine was running a little funky and when I pulled plugs on that engine they were "wet fouled"---black, oily wet.

The manual says use NGK BRP8's--somehow I was provided BRP7's and didn't realize it till I got ready to install them.

What is operating difference between the 7 and 8 heat range? Can I run these or should I just eat the cost and put the spec'd plugs in ??