I just purchased a 2005 21xd a few months ago and I had a problem a couple of times. It will not take gas the tank has less than 1/2 off tank and I can only get it to take 1/4 of a gallon. To get it to take gas I have to take the vent tube loose at the tank. When I take it off you can hear the air coming from the tank. I will then blow in the vent tube and some gas is present in that tube. Does anybody know why it is not venting