As a boy that loved toying with anything that ran on gas, I learned early on that gas goes bad. It was easy to detect as the altered smell made it obvious. I had lawnmowers that I used for cutting grass in the neighborhood and inevitability when winter ended, I had to disassemble the carburetors and run thin wire through all the carb passages to clean the varnish out. Why varnish? That is what old gas would leave behind. It would peel out like dried varnish. It looked like a piece of plastic lining.
The same would be true for my old dirt bikes. My Honda XL-175 and XR 500 would never run right at the start of the season. I could get it to run but they would not idle. Old gas and the varnish was the culprit. You can't just flush it out because new gas does not melt the varnish. Its there to stay until you physically attack it with a brush or wire.
Today things are worse due to ethanol content. Most of today's fuels contain 10 percent ethanol. I recently purchased a 2 stroke blower to use around the house and it came with a flyer explaining the risk of ethanol. They also packed it with a new oil appropriately named, Ethanol Shield (TM).
Ethanol is worse than old gas because it eats at the soft components in the fuel system. To add insult to injury, ethanol also attracts water which settles out of the gas only to be drawn up into the engine at some point. This all leads to a failure of some sort.
Consider using the GT Power Equipment product to simply pull out the gas when your not using the machine for more than a week. It's simple one handed operation allowing you to be sure that the next time you break out the machine and add some gas everything will be as good as the day you bought it. I squeezed the GT Power Equipment bulb twice to fill the blower and then twice again to put the gas back in the gas can. I fired up the blower and it ran dry in 30 seconds. Done and ready for next time.