DO NOT RUN IT!!!!!! Until you get bigger jets in there.
That dealership is a bunch of idiots, they were just following Toomeys instructions, which are jacked up.
You did not state your elevation, but let me give you my setup and you can figure out how lean he is from there.
I have T5s, stock carbs, no air box, running the Toomey 2:1 air filter.
I run at Glamis, about 300-500' elevation.
I run 370 mains, 30 pilots and Toomey needles on the 4th clip position from the top.
My bike runs AWESOME!!!!
I also have Boyesen carbon fiber reeds.
You are getting the popping and back firing because it is WAY lean.
I would also switch to 32:1 on the oil ratio. I run Yamalube and that is what I run at.
Good luck. Hopefully he doesn't have too many hours after his pipe change......