You’ll see them, probably as soon as this Saturday: panting, red-faced men and women, brows dripping, eyes ablaze. In their left hand a chainsaw, or more likely a leafblower, unstarted since this time last year.

Some will have assumed the position of internal combustion submission, machine turtle-backed on the ground, perhaps kicked a yard or so from its owner, whose left hand is comforting a right shoulder that, scores of starter cord pulls later, is screaming with pain.

We live in the age of ethanol. Congress passed the ethanol mandate in 2007 in an attempt to reduce greenhouse gas emissions and move the nation closer to energy independence.

Today, 40% of the nation’s corn crop and 30% of the soybeans grown wind up in gasoline. The wisdom of that decision has been debated ever since.

Ethanol, once added to gasoline, desperately tries to go back to being corn. Gasoline has a shelf life of about 30 days, 45 at most. After that it doesn’t just go stale like bread forgotten in a drawer. Its 87 octane rating has dropped to maybe 84, making the engine, if it starts, run rough. That’s bad enough, but ethanol absorbs passing moisture and begins turning into a gelatinous mass in fuel lines and carburetor bowls. Pull all day but the clogged machine won’t start.

The ethanol mandate is responsible, one small-engine mechanic said, for about one-third of his shop’s business. This isn’t waste on the scale of the nation’s non-system of health care, but its cumulative effect in lost time and wasted money is considerable.

Last year, an EPA report concluded that ethanol made from corn and soybeans is causing significant harm to the environment, chiefly by encouraging farmers in the U.S. and other nations to convert grasslands, forests and jungles to corn, soybean and palm oil production.

But adding ethanol is a cheap way to boost the octane of gasoline so engines don’t knock and farm-state politicians love the mandate. Consumers will be stuck burning ethanol-laced gas for the foreseeable future.

So back to those unstartable engines and how to avoid them, advice courtesy of local mechanics and the makers of small engines.

■Replace the fuel in engines that won’t start, including the fuel in the carburetor bowl, with clean, high-test gas treated with a stabilizing agent.

■Use ethanol-free pre-mixed gasoline in engines that are rarely started, e.g. pumps, chainsaws. It’s ridiculously expensive – $20 plus per gallon – but stays fresh for a year or more.

■Small engines require at least 89 octane but pros use the highest octane available. Always treat gas with stabilizer.

■When filling gas cans look for stations that use a different hose for each grade of gasoline. Otherwise, the first amount of gas – anywhere from a quart to some say several gallons – will be whatever octane grade the last customer purchased. To play it safe, put the first few gallons out of the pump into your vehicle and then fill the gas can.

■To avoid problems, run lawnmowers, snowblowers and other machines dry or fill the tank nearly full with ethanol-free gas or high-octane gas treated with stabilizer. Filling the tank nearly full allows room for expansion on hot days but reduces the amount of water from condensation and reaction with oxygen that causes fuel to go bad.

■Give up on machines and buy a rake, bow saw, scythe and a couple of goats.