I don't know where you are at, as elevation has alot to do with it. Remember that the jet may not be your problem. It could be your needle, or A/F screw. You need to find out if it is running lean through the whole band, or just at a specific point. When you know these things, come back here and I'm sure Jonnycheese might be able to make some suggestions. I know that when I first put my hurricane on, I had a hard time figuring out why I was getting "flat spots". Most of my problem was needle position, and had nothing to do with the main jet. As for dirty filters....clean it,how long does it take for cryin' out loud. LOL .