Yz125 problem

Hey guys question. So last week I bought my 2000 Yamaha yz 125 and it was running great no problems one day but then the next day I tried to ride it and it wouldn't start at all it sounded like the compression was weak but it still had some. Then yesterday we pop started it and gas and oil and just a bunch of fluid came spitting out of the exhaust I'm not sure what would cause this I left my gas on overnight after I rode it and that's where the problem started what do you think