helping a friend again... 2009 klx250sf

So a buddy of mine's kid has a 2009 klx250sf. he said his other friends moped is louder, so his dad made him a super nice, polished stainless muffler (he's a union steamfitter).

Problem is when they put that pipe on it sounds great, but they say it doesn't have the snot it used to. Obviously they need to rejet and just so happens my extra ones I have fit it. Now, they say it doesn't pop or backfire on deaccel, so does this mean that the pilot circuit is probabaly ok? I was going to start with going up a few steps in the mains and go from there.

Any thoughts? (besides I need to start cashing some of these favors in )