I bought an 05 sportsman 90 about a year ago. Before doing anything to it, I cleaned the carb, replaced the trans fluid, topped the 2 tank, etc. It has never been overly impressive as far as throttle response, but being a 90, I assumed this is normal. According to the manual, it claims it will run 30 mph from the factory, but I can't get it close to that! Anyway, as I used it, I could never seem to get the fuel delivery quite right. I have the service manyal and set air screw ro 7/8 out. It would run okay for about 10 minutes and then it seemed like it would just bog...eventually not taking any gas or taking gas but no power. I eventually bought a new carb from amazon... checked the settings inside compared to the manual...this is where I get frustrated. It starts fine, idles fine, and will take gas...for about 10 minutes. The longer it runs, the worse it runs...it will keep running, but you can give it full throttle and it doesn't have the power to move by 65 lb son. Seems like in neutral and reverse, it does fine. Eventually it will shut off and not want to restart. I was thinking tank wasn't venting, but no gas cap doesn't help. I was thinking coil or magneto, but I have spark when it won't start. If it sits for a half an hour, the process starts over. Plug is a light brown. Any help would be awesome. I am at wits end with this thing and my son is as frustrated as me!!