Hi, I have a 100% stock 2002 400ex, I still have the stock exaust and no plan or money to get an aftermarket slip on. The other day I took the tip of the muffler, and I really liked the way it sounded, it was a lot deeper then stock, and sounded great under a load. My question is, i rode it around quite a bit and it runs great, just as good as it ever did, but I know that taking the tip off makes them run more lean and I've also heard that 400s run a little on the lean side from the factory, so do I have to rejet if it runs good, or can I just adjust the carb, or do I even have to do anything. I also had the thought that cold weather will make it run more lean, and so once it gets to be winter here in oregon, will it start to run bad? Any advice is appreciated. Thanks in advance.