Exhaust question

A friend of mine is giving me his Zirri pipe, left hand, for my P2. Im just going to run it off the stock carb, just with the jets size increased. Ive heard good & bad things about this pipe. Some people have said that the revs decrease & others have had no problems & love these pipes. any thoughts.
Also, if I put a lightened flywheel on the bike do I have to increase the jet sizes for this as well as for the pipe?