LTZ 400 stalls
 

I've got a 2006 LTZ 400, standard, just removed muffler, the quad just stalled so i checked the quad, started it and it ran fine for a few km's and did the same, I let it cool down for 20 min again and started it and and ran fine again but gave the same problem again, then i let it cool down and checked the oil, no contaminants but something strange, the oil level was higher than usual and very thin, i put new oil in about 2 weeks ago.
On the left engine side it's got a small whole and some kind of fluid came out( rusty colour).
What could possible cause these problems?