I have a 17.5 hp b&s sears tractor. I can start it and mow for a short period and the mower will quit on me. I can start it again, but it will not stay running. I have replaced the air filters, fuel filter and fuel line. I have installed a new battery, disconnected the safety shut off switches, replaced the coil and the mower still stops on me after using it a short period. I would appreciate any help with this problem. Ty

Sounds like a fuel related problem.
I'll tell ypu something simple that a lot of people over look , check fuel cap and make sure its venting. The next time you use it if it dies loosen the cap then try .
I see this all the time.. Luck