Magneto expert needed

When you say rotor lined up with the post. Do you mean "exactly lined up"? From my understanding it should be just before so that when it snaps, it flies past the post. If I am understanding your description, it sounds as though it is firing past the post. Is there a gear set inside a WICO? That I don't know? I was always under the belief that they are a straight through shaft type of Magneto which is why they have the Impulse Coupler. I am guessing that maybe the Impulse Mechanism is on a spline of the shaft and MAYBE slipped a cog or three?
Just throwing it out there

Wico or prestolite does have a gear set. The rotor is about 1/2 in wide where it mates to the Spark plug brush. Mag is firing spark right at the beginning of the rotor contact. hard to miss it especially looking dead on to it, being in a test bench with a variable speed motor.
I think I have narrowed it down to the coil. Something just died as it was working so good before. The spark out of the coil will rarely jump 1/4 inch and was not blue.
Not working on a mag for a long time, I was thinking they have a really long blue spark. I got the mag off my 1941 parts tractor (4F867😎. Even with a cracked cap, on the test bench it will throw a 1/2 inch long blue spark after the plug wires on the test bench electrodes.
I have routed out the crack with a Dremell tool and JB welded it. Not even going to remove the cap. This mag is going back on my machine when the JB dries. It is the mag the parts book calls out

Wico magnetos have direct drive armature. Rotor is gear driven. Coil X5700C should check out at at least 8500 ohm and yes you should have a nice fat blue spark that should jump 3/8" +.
Condenser/capacitor should check out at 0.30 to 0.34 microfarads.

Thanks, I will ck that coil out.

Check that Wico s/n again.I believe it should be a 4S6470, not 4S6740.

Check that Wico s/n again.I believe it should be a 4S6470, not 4S6740.

The 1941 mag did not directly fit. Had to file out the mounting holes to a slot shape. The later engine the holes were not directly across the center line. The # on this mag is: 4/2 360A 408. Does that cross to a cat #? Wico mag coil read. 0.6 ohms

Cat 4S6470 = Wico XH2839= American Bosch NJK4/2 360 D410 used on the D318. 4S6470 was originally used on the 977D.

AB NJK 360 A408 = Wico XH2838=Cat #9H4479 used on the D4600.
These mags are not interchangeable on the D6 as the 408 series magneto is vertical mount on the D4600 and the 410 series magneto is meant for the D318 that has the tilted mount. The mounting difference affects the gravity controlled latching of the impulse mechanism.