Motorcycle Repair: 98 1200 carb backfire, k n air filter, loud pipes

Question
I purchased a 98 1200 sportster about 2 weeks ago and when I rev up above 2500 RPM's the engine backfires through the carb and stalls out. The modifications on the bike is an K&N air filter and the exhaust pipes(very load). Here is my question: Should I re-jet the carb or could it be some other possible problem?

Answer
jetting needs to be richer.  and very loud pipes or hi flowing pipes KILL all street horse power and torque. Some exhaust systems just CAN NOT BE TUNED.  no matter what jets are installed.  my advice to you is to get a exhaust system that works. your Harley dealer should not know this. You need a expert like my self to tell you. JOHNNY 602-705-7474