2003 Polaris Deep Snow Snowmobiles Service Manual, Page 135Get this manual
FUEL SYSTEMCARBURETION Float Chamber Venting
Fuel flows through carburetor by creating pressure difference between the venturi and the float bowlThe greater the pressure difference, the greater the fuel flowOn some models the float bowl is vented to the handlebarsThis provides consistent atmospheric pressure for consistent fuel flowIf the vent lines become kinked, plugged, or exposed to fluctuating pressures (under hood) the pressure difference will change, causing erratic fuel flowPolaris has airbox venting on some modelsThe vent lines are connected to baffle inside the airboxThis provides more consistent pressure difference between the carburetor venturi and the float bowl as the vacuum inside the airbox changesFor example, if the airbox foam filter becomes restricted with snow when riding in powder, the airbox vacuum increasesWithout airbox venting, the pressure difference would increase substantially, choking or flooding the engineWith airbox venting, the pressure difference remains the same, creating slightly leaner mixture to compensate for reduced air flow