Check to see if the pv blade isn't coked up too much carbon can be quite stubborn and make it stick ! Soak it in caustic soda you might aswell do the exhaust too while you at it, will make it sound a lot nicer failing that if the DT pv is run off a solenoid take the pv assembly off and do a test on a 12v battery to see if the magnet in the solenoid hasn't broken down. Hope this helps