Looking for troublshooter SearsLawn Tractor MODEL 917 on but cuts out in g?

19.5 hp. Need Troubleshooter guide. Can't find one on the net. Manual doesn't even address the problem. This tractor has had chronic problems. I had the Sears repair guy here three times last year. Close to $100 a visit. The symptom: starts and engine runs but when put in gear stalls/cuts out. First time it was safety switch under seat. Second time the rod that allows it to be pushed was in but there was something jammed. It took him 3 minutes to ID the problem and fix it. I need to know wht he knows w/o $100 visits.