EVERYONE has different experiences with motors but I would stick with Pine Baron. He's been there, DONE THAT. Every engine chat has a know it all and Mr. Smith seems to fit the mold. The fact of the matter is, EVERY engine is going to react differently to how you break it in or run it for that matter. Baron does have some experience to speak of and isn't to "proud" to say so. I work with motors every day and have brought some model motors back to life that have sat "gumming up" for as long as 9 years and Baron and a few of the others here are playing it safe and that's why they aren't having problems. Break it in with the stock muffler as your tuned pipe instructions say, you won't be sorry.