Hey everyone. New here. New gixxer owner. Had a few zx's. So I bought a 2014 gsxr 600 with 21k miles. It has only a slip on m4 and the previous owner removed the egsaust valve and put on a power comander. There are no fi lights on so I think that was also bypassed. So it runs great except that in between 3 and 5k rpm it hesitates a little. Probably because there's no back pressure right? Also it seems difficult to stand it up on the back wheel. Idk. So the other day I was riding maybe 20 miles and it was running fine then suddenly it was running bad. I think it was only running on 2 cylinders. I pulled over and shutdown immediately. Again no fi lights. I started it back up and the problem was gone. I filled up at arco just before, i try not to do that ever, My guess is intermittent coil packs. Somethings getting ready to go. Any help would be good. Thanks guys