Stalls sometimes?

Sometimes when im riding my foreman will start to sputter and then stall. When I blow air into my gas cap vent tube when its starts to sputter it comes right back to life. Ive ridden on some days when i will have to do this maybe every 10 to 15 minutes and other times i can ride for two hours and not have to do it at all. Ive checked the resistance of the air through gas cap and it feels the same as the gas cap on my 350 rancher. If anyone has any knowledge or suggestions i would appreciate it.