If you're going to change the exhaust for some power gain, then you should change the main needle, adjust the pilot air scew out to 2 turns and open up the air box. The whole point of an exhaust change is to allow the engine to breathe better. If you don't open up the front end (airbox) then the advantages aren't seen out the back end. As to the fuel economy I haven't seen and real change. My average has been the same with the mods I did. I have the Jardine pipe, Studabaker main needle, holes drilled in the air box, and I run the stock air filter. (it flows better than the K&N). The change in the bike was astounding. In fact when I had the bike at the dealer for some warranty work they asked me what I had done to the engine. They had never been on a KLR that would pull the front wheel off the ground with just some throttle, you should have seen the big eyes when I told the mechanic that I had a 16 tooth counter sprocket on it also. So yes, these mods make a huge differance to the machine.