I don't know if you are still active on here. I took a morning to try and get my Dad's old Wilderness 250 to run as well. It is doing the popping out of the breather. DId you ever remove the breather line from the exhaust and small one from the intake to the black box under the front? If so did it help it run better? I'm not even sure if I can get a new intake or the hose that goes to the breather box.