2004 Polaris Freedom, Virage, Genesis and MSX-140 Service Manual., Page 190Get this manual
PROPULSION Ventilation Troubleshooting
Ventilation results when air enters the pump inlet tract and is compressed by the impeller, causing reduction in thrust and an increase in engine RPMSmall leaks are often difficult to diagnoseSome possible sources of air are: 1An improperly sealed intake scoop is the most common cause of ventilationMake sure the scoop has complete bead of Marine Grade silicone sealer all the way around without any gaps or pin holes2Ride plate The ride plate must be completely sealed in the area around the intake scoop, and also in the area where the hull meets the pump cavity3Driveshaft bearing housing or through hull fitting If the drive shaft bearing carrier seals are worn or damaged, air may be drawn into the pump from the engine compartmentAlso inspect the through-hull fittingThe entire circumference of the fitting must be sealed to prevent water from entering the hull, and air from entering the pump4Incorrectly mounted pumpThis can be caused by an improperly installed intake scoop or misaligned pump (there should be no detectable gap between pump housing and hull)