I recently got my hands on a JD180 38" cut and a Kawasaki 540V about a late 90's model. Got it for $50.00 from a friend. Brought it home and after a little TLC it is running and cutting. My ?, It sounds like its knocking. It will knock for 5 or 10min and clear up for 5 or 10min. I ran it for about 5hrs like this, Ive checked the values at .006(JD gave me this clearance) and they seem to be good and after running it the oil still looks good(I have changed it with 30W). Ive also took off the PTO and ran just the motor and it still does the same thing. I'm not looking a perfect machine I just need something to pull my sprayer,spreader,aerator,etc. If it is something major I would think it would have gone in 5hrs at full throttle??