If you get suction at any time then the motor and filtration system are both good - if suction degrades as you adjust the machine then there's either a blockage or air is getting in where it should not.
If the motor runs a little faster and makes a higher pitched sound then there's a blockage. If the sound of the motor remains much the same then air is getting in where it should not.
Use your ears to work out what's going on...
Good luck...
Peccavi, December 2010
