Things to know about fuel and storage

Poor quality of fuel and how fuel is stored may result in these problems.
Exhaust valve(s) sticking.
Spark plug(s) fouled.
Hard starting
Vapor lock
Low power
Water in fuel.

Octane:
Octane is the rating of a fuel's RESISTANCE to burn or detonate. The higher the octane the SLOWER the fuel burns. So why is higher-octane fuel thought to deliver more power? It CAN deliver more power provided other conditions are present in the engine. The most important of those conditions are a higher compression ratio and more spark advance. Neither of which is available in our engines. Modern automobile engines on the other hand DO have variable spark (ignition) advance and can use higher-octane fuels but in most cases still won't make any more power. These engines also have an Engine Control Module (ECM) that gets feedback from a variety of sensors around the engine, driveline, and exhaust and in some cases, even from the brakes. These sensors vary the ignition timing as well as a host of other things. An ECM does not control our engines however. Not even the 445 L&G tractor with its EFI has the ability to vary its ignition timing. A gasoline engine used in an application where engine speed is changed constantly should have the ability to vary the ignition timing. This is critical because regardless of the speed of the engine, the fuel will always burn at the same rate in the combustion chamber.

Therefore as engine speed increases, it's important to start the fuel burning sooner. Notice the term "burning" is used. When fuel is ignited by the spark plug it does NOT explode like so many people think, it starts the fuel burning. That burn is actually a flame that has a "flame front" and as that flame front travels across the top of the piston and throughout the combustion chamber, (referred to as flame travel or swirl), it is releasing energy by causing a very rapid expansion of the burning gasoline and oxygen. This is the energy that pushes the piston down and rotates the crankshaft. Now this is important; the burn is started BEFORE the piston reaches top dead center (BTDC). You might think that would push the piston back down in the bore causing the crankshaft to turn backward but remember, we only START the burn at that point. As the gasses continue to burn, if the timing is set correctly, the gasses will be expanding at their fastest rate when the crankshaft has traveled beyond TDC about 20 degrees or so. This will exert the energy on the crankshaft at the most opportune time so as to get the most power from the engine. Compare this to riding a bicycle. You can exert more energy on the pedal and more power to the wheel ATDC but after about 90 degrees or so, the power begins to drop off. But if you begin to push the pedal down BTDC with much force, the results could be painful. That brings up the next subject

Pre-ignition (sometimes called knock or ping due to the sound it produces), is a condition where the fuel ignites too soon and actually DOES try to push the piston back down in the cylinder before it reaches TDC. This can be damaging to the engine and drastically shorten its life. Pre-ignition can be caused by a variety of conditions in an engine, i.e.: octane rating too low, hot or glowing pieces of carbon in the combustion chamber acting like a spark plug, overheating, or too much spark advance.
All John Deere Lawn & Garden equipment is designed to run on 87 or 89 octane fuel.

Freshness, storage and seasonal differences
Freshness of the fuel is important because many of the chemicals in gasoline are very volatile and will evaporate into the air, leaving only the heavier elements behind. These heavier elements may not be as combustible and can cause a "gumming up" of the fuel system.

Fuel without a good quality stabilizer added to it, should be stored no more than 30 days or so. A good way to keep track of this is to write the date of purchase on the container with a magic marker. When 30 days has gone by, add the fuel to the family car when the tank is half full or better. This will dilute the fuel with the fresher fuel in the tank and not effect the performance of the car. (Provided the fuel is not too bad.)

A plastic container is preferred over metal because plastic is not as likely to "sweat" or cause condensation of water inside the top of the can.

There are seasonal differences in the blending of gasoline. In warmer weather, heavier chemicals are added during the refining process to keep the fuel from evaporating or causing vapor lock as easily. In colder weather, lighter chemicals are added to aid in cold weather starting.