2007-2011 Polaris IQ Snowmobiles Service Manual, Page 165Get this manual
Fuel Systems StartingEnrichment System
The starting or enrichment system provides additional fuel required to start the engine in cold conditionsA cold engine requires more fuel to start than warm engine because the fuel mixture tends to condense on the intake and cylinder walls rather than vaporize as it would in engine at operating temperatureMikuni VM carburetors use plunger-type starting systemWhen the choke lever is engaged, springloaded plunger is pulled away from the starting circuit orifice allowing additional fuel to be drawn out of the float bowl along with the fuel drawn through the pilot jet systemBecause the starting system provides fuel not metered by the pilot or main jet systems, it is important to verify the plunger properly closes when not neededA starting system that is stuck open or improperly set will cause rich running and heavy plug foulingLikewise, plunger that is stuck closed or does not open far enough will make starting cold engine difficult
Air Screw
The air screw controls the amount of air that is mixed with the fuel drawn out of the float bowlThe more air allowed to mix with the fuel, the leaner the fuel mixtureTurning the screw in (clockwise) reduces the amount of air, while turning the screw out (counter-clockwise) increases the amount of air