Left gas in lawnmower all winter
You'll want to totally drain the gas tank and dispose of the gas you remove. Then, pull the spark plug and check it to make sure it's not gummed up. (That's the problem the old gas will cause - components in it break down and can coat some surfaces in the engine with a gummy or varnish-like substance.) Refill the gas tank with new, fresh gas - I'd recommend only about 1/4-tank in case you have to dump it again - and I'd add a little "dry gas" like you'd use for your car when you have water in the gas. Prime the carburetor and give it a few pulls with the throttle/speed control in the START or fast position. Good luck!
In the fall, you can go to places like Wal-Mart, ***** , etc. and get stuff to stabilize your leftover gas. You can normally find small packets that are sized for small gas cans or you can find larger amounts that require you to measure and mix. They come with complete directions. I hope this helps some - regards! Jim D/Heathsville, VA
Sharpen the blade also. If it is self propelled you might need to grease the drive wheels also.
Joed is correct that you can try and start it. The worst thing you'd do is possibly flood it, and you'd have to let it sit a while before trying again. As I said, I left mine on my back porch all winter long...we had probably 4 feet of snow over the season and several weeks of below freezing temps. The gas tank was totally full. I'd changed the spark plug and the oil last fall, so I knew they were good to go. I put a new blade (old one was beyond sharpening anymore) and new air filter on it and primed the carb. It cranked over on the first pull...I've used it 3 times now and no problems at all.
I hope this helps some - good luck! Jim D/Heathsville, VA
I never drain my gas out and it always starts the next year. Going on ten - twelve years now. Maybe I'm just lucky. Maybe the advice to drain is overkill on preventive maintainance.
Next year, either drain it or use some stabilizer when you put it away for the winter.