This will get the timing close:
1) Make sure the ignition switch is OFF
2) Open the distributor and check where the rotor is pointing. If you haven't messed with the wires (or you're sure they didn;t get mixed up), turn the fan blade until the rotor points roughly in the direction of #1 (should be able to turn it without removing the plugs)
3) Go around to the carb side of the tractor so you can see the timing pointer. Move the fan so the timing mark on the pully is lined up with the pointer. This is when the spark should fire.
4) Go back to the distributor and check the points. Rotate distributor until the points just open. That's when it will fire.
This should get it to within a few degrees of correct time (depending on how close you can guess when the points break).
Chances are you just have it way out of time, that's easy to do since turning the distributor just a little moves the spark a lot.