As far as the jets go I'll reach into the way back machine and give you this as it's a little late to type it all out again....
131 Main Boards / Tech Forum / Re: Keihin Carburetors on: November 15, 2005, 07:56:20 PM
I just removed the slow jets on mine. They came out easily with a piece of leather and slip-joint pliers. I wrapped the leather around the jet to protect it and then gently twisted with the pliers to loosen it a little. Then I gently pulled straight up. I was actually surprised at how easily they came out after reading Honda's warning in the shop manual. "The slow jet must not be removed since it is a press in fit." Yeah...right.
Mike
Changing the exhaust may or may not require a jet change. It depends on what the exhaust is. Mods to a 650? The sky and ebay are your limit. I for one don't really know what's available as far as after market for 650s. Good luck...
Mike