I have a friend at work that is having problems with his mower. Now he has asked me about it. I told him what I thought but thought I would try to get some info from some others. It is a 17.5 hp briggs model 313777, type 0124-E1, code 00020420. He said it ran fine. Died & won't start,he did get it to start once. It turns over until it hits compression then it stops. He has replaced the battery & starter. Has used jumpers on it. It can be turned over by hand. My suggestion is the flywheel key(I think he said his daughter had been mowing with it). I was wondering about a compression release internally in the engine. Is this a possibility & if so can it be checked without taking apart. As I said it can be turned over by hand & can still be turned past compression by hand but not by the starter. This is all 2nd hand info,have not actually looked at the mower. Anyone with ideas/suggestions I would like to hear them. Thanks