If your running 148/165 that's way too much of a difference, you should only be at 1 size difference. Since you say it's bogging at low rpm it's probably your left carb. Anyways, did you ever clean your carb? i know it may sound stupid, but people forget the simpliest things. Secondly, look at your spark plug...is it new? or have you had it for awhile. While your jetting your quade, get a new sparkplug, run it for a little bit and check your plug. that' will tell you if your running lean or rich or just right. ***rather be rich then lean***. Secondly, check the resistance to your spark plug wire, make sure it's within specs. Check your coil and see if it's firing correctly, Do you still have your parking break installed? becuase if you do, disable it and see if that helps out any. It might also be your cdi box. Might be putting on an rev limiter when it's not supposed to. See if you can borrow someones and check it out. Also check your stator. I've heard of wierd tihngs happening when the stator goes out. Check your valve lash. Make sure that's in specs as well. Check these and see if that works out for ya