Hope someone can help me. I have a John Deere 425 with a Kawasaki V twin liquid cooled 20 hp ohv that is about 10 years old with 400 hours on it. Starting at the end of the mowing season last year it started to lose power everytime I mowed. It takes me about 2 hours to mow my lawn and it happens at the end of the mowing session each time. First I notice the power steering starting to freeze up or become hard on turns. Then I notice if I stop the mowing deck when I engage the PTO the deck doesn't respond instantly but rather sits for a second or two and then gradually starts running again. Finally, at the end of mowing the lawn, if I put any strain on the deck it just bogs down. It runs perfectly when it is first started and for a half hour or so, then all these symptoms start up.

I have taken good care of it, and done the maintainace faithfully, annually... except this year, I did not change the spark plug nor did I buy a new air filter, just cleaned the old one. But could those two things also affect the power steering as well? If so, wouldn't it do it right off the bat and not after running for a bit? Also, they wouldn't affect the PTO and make the deck take longer to engage, would it?

Any help would be appreciated, praying it just isn't that the engine is plain worn out!