MMC

All of these suggestions have been great. I was thinking there was a vent line elsewhere, but the one on the top is clear. the air box has one, which is capped, so I guess you'd open it to drain oil if it's necessary at the time. The 15-20 minutes is pretty consistent. I could see it being something electronic. Somewhere I read about checking the stator. Some of that is beyond my backyard skills. I'm near Gainesville FL, and the local Suzuki place said that they don't work on anything that old. It's a 2000. I haven't find another place to take it to yet.

It seems to be 15-20 minutes, riding or idling. I replaced the filter, but do see oil in it. I'll have to locate the tank vent line and check it.

I have a Suzuki Quadmaster 500, that I got from a customer. It has less than 400 miles on it. I think I put most of the miles on it, so they sold it to me. I used to drive it a few times a year, treatinjg the gas or emptying it when I could. I relocated and wanted to get it running again. It will start with little trouble, then run for 15-20 minutes, then start to chug a bit, then finally stop. Sometimes I can start it again, but it doesnt continue to run long after that. when I first opened the oil filter when I moved, it was drenched in oil and fell apart. I went and replaced it with a OEM foam filter. I notice now, when it does stop, there is a small amount of oil on the bottom the air filter box, and it's clean oil. I had recently changed the oil before I moved. Each time I clean that up, I go through the same process. It will run, and I can drive it for a bit, but then it slows down and stops. Any suggestions? I am not an ATV mechanic by far, but can work on most of the stuff I own. I did have trouble finding a dealer who would work on it. One local one, said "We dont' work on stuff that's over 20 years old" It can't be because of parts, I just laughed.