I just got a new Powercore 2 for my 03 KX250. I have an FMF Gnarly pipe on it right now. I rode it today and its sacking out when I go wide open, its also popping after the sacking. It has never done this before. I know I had to rejet my bike when I put the Gnarly pipe on but do I have to rejet my bike for the new slip on muffler? has anyone ever had to do this? My bike was running great before I got this new exhaust.... Im in Montana at around 3000 feet in elevation. Please help me out guys!!!!