I just got a 500 Fourman 4x4 a couple months ago.When I was overlooking it the first day I noticed in my airbox drain a oily fluid inside of it.After doing some observing I came to the result that the factory when prepping the atv sprayed or poured way to much air filter oil for the foam cover and it was in the drain,all on the sides of the airbox and actually I found some residue inside the carb.You didn't state if your bike was new or an older atv,so if you just bought it new it could be the same situation.Takes a couple wrags and cleaner to remove,good luck!!!