98' XR600 - Have just installed an FMF Powercore 4 pipe, removed snorkel and ground header welds and as the beast still had stock jetting I started with a 155/68 setup and the bike was wicked, heaps of power but didn't respond quickly when I let off the throttle, also as it ran best with the fuel screw all the way in (I only ran it like this for about 5 mins) I figured it was too lean. I then tried the same mj with a 65 pilot and it didn't run nearly as good and coughed and farted a fair bit more. I carried out both the adjustments correctly I believe so my question is, should I try the 68pj again with a 158mj or somethin similar. Jetting is not my specialty and I just want to get it right. Any suggestions PLEASE??