jets

[His Dudeness]

In a single word: no.

It's a bit trial and error, but jets are cheap. Might be a ball ache to do though, buying some, fitting, repeat. I'm surprised it's caused a flat spot though - have you changed the air filter too? And have the carbs been balanced? My tail can breathes VERY freely, and I have a K&N fitted. I've debated doing the jets too, see this thread for some idea's, although remember - he has cone filters fitted:
http://fazerowners.yuku.com/reply/216863#.U_fSneiP5hJ

You breath out of a tail? :eek I'd check that everything else is 100% before going down the rejetting route. I'd also stick the original exhaust back on and see if the problem does actually go away so you know for sure it's the exhaust causing it