Originally Posted by Grinder

I would just stick with the C7 plug that comes in the engine for break in. You can use a 6, but it is not mandatory. The 35+21 takes a while to fully break in. Follow my instructions, and you should be fine.

It is OK to break the engine in on 25% nitro, just keep the engine rich in the beginning of course. To break in the engine on the break in stand, I use 10% nitro, and 16% oil. Then on the track I use regular 25% nitro, with 9% oil fuel that I will race with. The extra oil used on the bench makes the engine run hot, and flame out if you use it on the track.


http://murnanmodified.com/breakin.php