When you modify things that helps your quad "breathe easier" which helps the air flow through the motor such as air filter, exhaust, port work and such you will need to adjust the amount of fuel you introduce as well... You do this by raising jets. The bigger the jet the bigger the hole in it for fuel to make up for the increased air flow... Its a fine balance that will probably take a semi skilled person or alot of research to get the proper ratio.... If you have too small of jets you will run " lean" resulting in some serious issues... If you have too big of jet you will run "rich" and you will foul out spark plugs regularly...