This mower has been bullet proof until now.  The problem started with the PTO disengaging which I eventually determined was a faulty switch.  I disconnected the reverse switches and wired them together and installed the new PTO switch.  That now works fine, but now when I engage it the motor has a noticeable rpm drop.  When I get into heavy grass it bogs down.  The govener moves freely but but does not rev up the motor.  I did notice that the voltage drops down to around 10.5 when the PTO engages.  I've check fuel lines and filter.  What do you suggest?