In Reply to: 1939 Ford 9N Tractor posted by Jim Mortensen on May 16, 2017 at 16:05:38:
If your fuel and spark test check out OK, try unhooking the exhaust pipe from the manifold and see if the engine will run. A plugged exhaust will let back pressure build up to the point that there will be no intake flow into the cylinders. If you let the engine sit overnight, it will start and run for a short time. Now, with the pressure built up in the exhaust, it my fire but not run. If you continue to attempt to start the tractor, it will not even fire.