Quote from Kawasaki ATV Service Bulletin #04-03:
"On some eligible units, a severe backfire noise can be heard from the air cleaner housing when riding at low speeds."
Kawasaki has issued FAR campaign for units in the below specified VIN range:
VIN: JKAVFDA1_5B500001 ~ 513500
VIN: JKAVFDB1_5B500001 ~ 504641
Under this FAR campaign the front carburetor will receive an updated jet needle that matches the one in the rear carburetor. This fixes a low speed lean condition that certain units exhibit.
Any further questions can be directed to the service department
