Zixxer,
I just didn't like the way the 97T plug ran for me, plus I a bunch more to choose from that ended up being better. The 97T says its a medium plug, but for me it didn't act like a medium, more like a hot plug. It could have been just me that day. I tried a bunch of different plugs, one because I had some already and two, because maybe I could get one running well enough for me even though many said it didn't run well in their motors.
What I have come to know is that the the Ex-Tech #5's and P4's work the best for me. In a pinch I can get by with a P3, maybe more so if the weather is cold. Rossi #5's worked, but didn't seem to last me that long and the #6's were just way too cold. That is unless the outside temp was above 90 to 95 (in low humidity were I am at). Just what worked for me. So far both of my mills have been trouble free tuning wise and just run. Fast. Makes the race day that much more fun when you don't have to keep chasing the tune. Granted the tune is not always at the best for a given day, but close enough not to have to mess with it. I ran almost the whole season at the "Fat" settings on the carbs. Leaned it them out to the "Tuned" settings towards the end. Didn't think the motors could get any better, but they did.