whats up peeps!! new and have some Q’s

Hello everyone!! Im new to the Polaris world and purchased one today. I have an unknown year trailblazer 250.
First Q is how do I find the year and VIN for this quad? Ive searched everyone on it; under the seat, along the frame, no luck except for a sticker that was dated 1997… I think.
2nd – I rode it all day before the purchase and the only issue I had was before we trailered the dang thing, it started loosing power. Was running amazing, starting first pull(starter is dead), then as I ran through some muck, it took some extra beating getting out, neverr held it full throttle mind you, was bogging when giving it throttle and hasnt run since. Had to be pulled back to camp and it seems harder to pull start than before this issue, what I mean is that it takes extra effort to pull the rope. I cannot get it to even try to start, sputter or anything. It has spark and can see decent light through the airfilter. The old spark plug was covered in gas is why i put a new spark plug in it. I dont know what the appropriate plug is, put a BP5ES NGK because that is what was in it. I only have seen an oil line filter, no fuel filter to even suspect a clogged fuel filter. One thing i have noticed…. and scares the crap out of me… is that the oil tank was full when we started that day. After hours of riding, the oil tank is still full to the top. I have no experience in oil injection, but im not a dummy and believe that no oil was used the entire time. So…… my question….. Is there a way to check the oil injection system? and has anyone else run into this issue? thanks for yalls time