I have a 99 mxz 600 that I have had since it was new. Yesterday I took it out for the first time this year. I did clean the carbs and clutches as normal before riding. It ran fine for about 3 hours. At the end of a field after being on the throttle, it was like I shut the kill switch off. Atfer rolling to a stop I checked the DSS switch and the kill switch and it started first pull. It did this three more times in about as many miles, starting right back up every time. After pulling into the yard, I pulled the plugs. They were lighter than I think they should be. I was told that this machine will shut itself off, if it is too lean. The airbox and carbs are off now and I see that there is a filter in the oil line between the tank and oil pump. How often should this be changed? Any help would be greatly appreciated. I am headed to Maine soon and need to get this corrected! Thanks in advance.