Chainsaw Repair

On my 372xp the vent was getting iced up from the outside sawing in snow at zero temp outside. Anyway how the vent worked on mine there is a check valve at the gas tank that only lets air into the tank through the rubber hose, won't let air or gas out. So when I bring the saw inside and it warms up it builds pressure inside the tank because I can hear it escape when I open the gas cap. You can hardly tell if the check valve is plugged by blowing on the hose with your mouth, with gas cap off and tank empty. I think because of the small orifice in the check valve, But I could hear the air come through when I blew it with a air gun at a low pressure. If you can blow air back out the gas tank through the check valve the check valve is bad. Mine the hose where the vent air sucks from under the saw was getting iced up and acted like it was running out of gas after some hard cutting then wouldn't start again right away. I crack open the gas cap and all was good again for a while until the gas tank sucked itself into a vacuum again. It is a **** cutting in deep snow.