We just bought a JD L-120 used 6 weeks ago. It ran great, the guy did the oil change and sharpened the blades and did all the service work up to date. We mowed our yard a total of 6 times (all grass less then an acre) and it has 464 hrs on it. We just mowed and getting it put away and all of a sudden sounded loud and has no power in reverse. Checked the spark plugs and looks to be running on only one cylinder. HELP! My husband is mechanically inclined but never worked on a mower so looking for advice. We went by a JD dealer to get a manual and of course doesn't have one.