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?