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Old 10-03-2011, 05:44 PM   #4 (permalink)
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Location: Western Wisconsin
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honda cb125 - '74 Honda CB 125 S1
90 day: 79.71 mpg (US)

green wedge - '81 Commuter Vehicles Inc. Commuti-Car

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Most modern cars have sealed gas tanks so very little fuel vapor leaks out, they also have fuel injection so there is little to no air in the rest of the fuel system.
Motorcycles that have gasoline that is 9 months old or more tend to have issues because there are so many vents in the carburetors and the gas cap is more or less an open vent, because of this the volatile part of the gasoline evaporates and escapes leaving behind varnish, this is often made worse with ethanol in the gasoline because the alcohol sucks up water out of the air the ethanol then easily evaporates leading to water in the gas.

So I figure if gasoline is in a can or tank that is vented it has a shelf life of 6 months before issues start to show up, if it's sealed in a safety can, or the gas tank of a vehicle with fuel injection it's good for a year or more.

The motorcycle shop that I used to work part time at has a lot of motorcycles come in every spring with bad gasoline and I still get calls from friends who have lawn mowers that have year old gas from a gas can put in them and don't want to run, change the gas and they run, put that old gas in a fuel injected car and it will run as well.
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