I am running a t5 172 reedvalve with a pipe design bullet exhaust 19 bhp 21 tooth clutch I am using b9 plug would I be better running a b10 as it a very revy engine cheers chris
sorry this question can only answered by yourself.
The proper spark plug is something which has to be evaluated in accordance with the main jet in your carb and for shure with observing the "spark plug face".
So it is advisable to perform a jetting procedure and check the "spark plug face".
If the jetting seems ok, but the B9 looks to have become too hot, maybe a B9 would be better.
Otherwise, if the main jet is the right one, and the plug seems ok, then keep it.