I have a Yard Machines rider model 13A1660F000 (2003) that just started to act weird. I have owned this mower for 13 years and have never had this problem before. The first time I used it this year it started ok and ran normally for the first half hour. Then when I got off the mower to open my gate to the backyard, it started acting up. I disengaged the blades and took it out of gear so that I could get off it and leave it running (normal procedure). At that point the engine started to miss. It would continue to run but still miss. Then when I got back on and re-engaged the blades, it went back to running normally. Thereafter every time I got off the mower it went back to missing but continued to run until I re-engaged the blades and then ran fine. I am wondering if there is a safety switch somewhere that might be out of adjustment or has a loose connection. I have no literature on the mower to look at a parts list unfortunately, so I have no idea what to look for. I am hoping someone may have experienced this same problem and can point me in the right direction to fix the problem.