| Hi,
Have to agree with that already mentioned, reiterate the "best way to shut it off is to cut off fuel and let it burn dry" and add my "two cents worth."
Snowthrowers are rarely used in my area because it snows little. The most common use here is to clean chicken coops and stables. That said they are designed to start in cold weather and are therefore extremely sensitive to flooding in moderate temperatures. I only know three people who have them for snow and those see use only every few years. They have landscaping contracts that require them to clean sidewalks of snow. One of them almost always floods his even then.
Another thought beyond those stated is to do something some friends do (some at my recommendation) who have equipment that is infrequently used, ie snowthrowers, generators, chipper/shredders, etc. and that is use good quality fuel (bought where you know they sell a lot), stablize it, shut off with fuel shutoff valve and after running fill the tank full. That final one is because it reduces the amount of air in the tank, and air is part oxygen which is what makes the fuel go bad. The less there is, the better off things are.
Peace,
Clarke | 
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