I just got done with ther break in of the GRP .21 tuned version, mounted in my MBX5T, 1st off any of you that said it won`t pull a truggy can stop posting on here, you don`t now what you are talking about.This motor rips
I had to start ther break in with the OS P3 plug, it wouldn`t stay running with the 5 or 6 being so rich, I switched to the #5 when I was finished with the break in and had no fuel leakage at all, maybe I was lucky. either way I like running it with the #5 we`ll see how she lasts.

good luck with all your GRP`s