My uncle is rebuilding an '88 trailboss 250 that he was given. It had a blown motor, so he got the motor rebuilt, but there is a threaded hole on the bottom of the case. When he fires the motor, it's sucking and blowing air from this hole. That tells me that this hole needs to be plugged. What goes in it? Is it just a bolt, or is there more to this? Here are the pics:
http://atv-racing.com/trailboss

Thanks!!
Fish

 

Its the crankcase drain hole. It needs a threaded plug with a gasket. Runs kind of crappy without it.