You may need to re-time the drive gear. Also, there are two procedures to time a mag. One is done at Top Dead Center, which I think is what the other post describes, and the other is done at 30 degrees of advance (FIRE when looking at the inspection port). I prefer the latter. My instructions below assume you have a FMJ mag.
1. Make sure the internal gear is timed properly (I think "C" is correct per the other post). 1a. Since you think it was out of time before, mount the mag to the drive, and remove the mag and drive shaft from the engine (the gear on a WC does not have any timing marks, at least mine didn't). I don't remember if you have to pull the governor apart for this or not. My WC and manuals are in Nebraska.
2. Make sure the #1 piston is on the compression stroke, and line up the "FIRE" in inspection port beneath the tractor.
3. Removed the distributor cap. Just before the Upper Left spark plug post (#1 plug) there should be one or two bars cast inside (with a small 4 and 6 (4 cylinder or 6 cylinder)). Rotate the drive gear BACKWARDS until the rotor lines up with the #4 bar. 4. Re-mesh the gear with the camshaft and make sure you are still lined up on "4" bar. You may have to remove and re-mesh accordingly since the gears are bevel cut, just make sure you are rotating the mag backwards.
5. Tighten the assembly and reinstall the governor if removed in 1a.
6. If it is backfiring when you try to start it, you might be 180 degrees out of time...