I have a 16.5 HP B&S tractor, model 917.271640 that won't turn over. It will start when jumped. Thinking it was the battery, I bought a new one and it still won't start. I jumped the new battery and it started.

W/o the jump, the flywheel turns a bit, then stops. Any ideas??
Thanks

On the surface it seems like there isn't enough cranking power to turn it over since jumping it with what is likely a stronger battery or engine seems to work. Is the new battery fully charged? Is it rated with enough cranking power for the Tractor?

If all of the above are good, then it sounds like a loose wire between the ignition and the starter motor or flywheel. Could be a grounding issue also, since when you jump start it, it's likely you reestablish the ground.

I would check all your wiring, it could be your ignition switch is going bad too. That might be something to check into.