2003 Polaris Deep Snow Snowmobiles Service Manual, Page 134Get this manual
FUEL SYSTEMCARBURETION Explanation of Gasoline Volatility
One of the sometimes misunderstood properties of gasoline is its volatility, or ability to vaporize at different ambient temperatures and altitudes during the yearWhen gasoline is blended, it is given Reed Vapor Pressure (RVP) number which reflects its ability to vaporize or mix with air at given temperature rangeGasoline vapor pressure is measured by putting sample of fuel inside closed container and applying specified amount of heat to the container for certain amount of timeRVP will vary from about 7.0 PSI during the summer to approximately 13.5 PSI during the colder monthsService stations selling large volume of fuel will normally have the correct blend to work well at all times throughout the year in their local areaWhen the weather is very cold, gasoline must be able to vaporize very quickly in order for an engine to start and warm up properlyIf summer blend fuel is being used in the winter, little or no vaporization will occurDroplets will form causing flooding and very hard startingIf winter blend fuel is being used during the summer months, it may cause vapor lock (boiling fuel) inside the fuel lines, fuel pump, or carburetorThis will cause warm engine driveability problems and hard starting when warmSome states are limiting the Reid Vapor number to 9.0 PSI year around to help meet evaporative emissions standardsLow Vaporization Rate Warm Weather