Every year, a number of snowmobilers are surprised to learn how quickly gasoline deteriorates in their snowmobile. Either the sled doesn’t start after a...

Every year, a number of snowmobilers are surprised to learn how quickly gasoline deteriorates in their snowmobile. Either the sled doesn’t start after a “normal” period of storage, or it won’t idle (or run properly) after coming out of storage, or the sled doesn’t start as soon as it gets cold out.
Here’s why. Gasoline can stay fairly fresh for a while, if stored in a sealed, non-vented container. This is to keep the gasoline’s “light ends” from evaporating. The light ends are what allow the fuel to ignite easily at first start-up when the engine is cold.
A snowmobile’s gas tank and fuel system is vented to the atmosphere, so it is far from sealed. This fact means the gas in your sled is really only “good” for about 30 days in this type of storage medium, an unsealed container. Sleds are usually stored from Spring to late Fall, usually in warm and humid conditions and under wide temperature swings. This is why a sled typically experiences some of the worst fuel-related problems in all of motorsports when the fuel is left in it for extended periods of time.
How does this happen? The tank actually breathes during the wide temperature swings. Light ends evaporate and saturate the air inside the tank. The tank warms, and the air-fuel vapor is pushed outside the tank through the vent. Then the tank cools, and draws back in fresh air. The cycle repeats the next time the fuel warms up, light ends evaporate, saturate the air in the tank, vapor is pushed out the vent as it heats, then fresh air is drawn back in as the tank and gas cools. Slowly, the gas goes “flat”.
This means that keeping the tank full and reducing the temperature swings (store at a stable temperature) will minimize the loss of light ends. Minimize, not eliminate.
The other problem with evaporation of the fuel is crap known as “soluble gum”. When gas evaporates, this is the sticky goo left over that plugs carb jets. It is formed by oxidation of certain hydrocarbons that combine slowly with oxygen in the air and form gum.
Fuel manufacturers are required to contain a deposit-control additive. If the gasoline contains a lot of soluble gum, then the normal amount of additive may not be enough to clean away the left over gum from storage. This is why you might need to treat the first tank of the year with an extra dose of cleaner if a machine displays drivability problems after being stored. From a reactive stand-point, we’ve found a product called “Schaefer’s Neutra” to really do the job when you need to clean the fuel system. A 12 ounce bottle added to 10-12 gallons really makes a difference. Dissolving and removing the gum, varnish and internal residue is where this product shines. It’ll take a lot of the carbon off the power valves as well and out of the combustion chamber, but should be used as an occasional cleaner rather than on an every-tank basis.
From a proactive stance and as a preventative measure, placing a Fitch Fuel Catalyst into the fuel tank will keep the fuel fresher longer, continually “cracking” the longer chain hydrocarbons down into “light ends” so the fuel stays able to easily ignite after periods of storage.

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