Not too long ago I put a stock pipe back on due to sound laws. My warrior had a Cobra exhaust on from the previous owner. It sounded like ****, didn't idle and ran super rich. I always thought that the previous owner put in jets that are too large. Well today I pulled my plug after a few hours on the stock exhaust and its running perfect. The damn Cobra exhaust was more restrictive than stock, causing my quad to run rich. I find it hard to beleive but its hard to argue the facts. I am definitly glad I switched.