Hey Dustflyer,
I see that you took the advised...
By the way, I would recommend you use a McCoy #9 instead of the K&B plug. The K&B 1L will not hold up to Jett .50 performance and will blow the element easily. Your best bet is the McCoy #9 because it was designed for High RPM use. I use it all in my Racing Engines with RPM ranging from 19,000+ to about 30,000 for the FAI .40 and they're great. I can get many run with each plug, but I often change one plug for every flight to get the optimum performance for racing. Got to keep the edge you know.
Hope this information help!
Sam