I had no trouble at all breaking in this engine. It did take longer than other engines I've had. I didn't use the break-in shim, I wanted to, but the first head bolt I tried to remove I stripped the head hex. My fault, worn wrench.
I have a dual motor starter box, I'm sure that helped. I just made sure that the engine was hot enough before I started it. I had to drain the pipe after every tank as it was full of spent fuel and oil. I think the JP-4 is a good pipe for break-in because it is a gas hog.

Here's a link to the GTR 2 in a MBX6-T just before it dropped it's nuts (still rich) on our new layout. Not my best laps, still learning the new track with a new surface. I start out 3rd, take second for a little while, and end up 3rd of 3 or last. The other two guys are 2 of the fastest 3 at the club, I'm still learning!
http://www.youtube.com/watch?v=CV8PCfF5We4
Cheers
Brian