Bridgestone Battlax BT016 is what I put on, I don't think there's any need to change the size of the front unless you really want to. As far as the jet kit backfiring, I believe those are isolated incident - I believe the majority of the people on these forums have either shimmed their needles or installed a jet kit without a problem, take a peak here:
http://www.ninjette.org/forums/showt...highlight=Shim that is how a lot of people have gotten away without actually buying the jet kit, they simply use a few washers. The only difference you'll have is that it can't be adjusted quite as precisely as the actual kit.