Magneto

O.K. trying to get the '39 B timed right. The mag drive lug is horizontal at #1 TDC. It will start and run (rough) but timing light shows firing at about 5 o'clock instead at LH impulse mark.(3 o'clock) No way to get enough mag adjustment to fire in the right area. I notice mark inside of mag is all the way to one end of the hash marks. Wrong direction to retard spark.It is a WICO X. Probably something foolish I am missing, but ???? THANKS for any help!

The marks on the mag should be 2 1/2 marks left of center

The marks on the rear of the mag have to do ONLY with adjustment of the Lag Angle and they affect ONLY the static start/impulse timing THEY HAVE NOTHING TO DO WITH THE RUN TIMING.

To set the lag angle, its necessary to start with knowing which drive cup you have, it may be 2 marks to the left and it may be over 4. You can not set it by guessing, you need FIRST to know what drive cup you have...........

John T

You are missing something foolish indeed. You've mixed up the timing marks you should be using. The IMPULSE mark is for setting the starting timing using the dog kick out scale on the inside of the mag. The IMPULSE mark at 3 O'clock is Top Dead Center (TDC). The mag should trip (IMPULSE) just after the flywheel lines up there. You don't use this mark with a timing light. The flywheel impulse mark is in the wrong place to use it conveniently with a timing light to set running timing with.

While running you want it to fire at between 28 to 30 degrees Before Top Dead Center (BTDC). That position would put the flywheel impulse mark way down at the bottom right part of the flywheel circle. John Deere neglected to give us a mark for that one to use at the 3 O'clock position so you'll have make your own on the flywheel to use with the timing light. You turn the mag in it's mounting bolts to adjust this timing setting. By rights, this is the timing setting to set right first and then you can work on the dogs and their kick out plate setting to get the mag to impulse just after TDC in order to not kick the starter or flip the helper end over end.

The dog kick out plate is in effect the ignition retard setting and it should be little less or equal to the degree advance that you want the tractor to run at. So you set the mag to fire at 30 before TDC and you set the dogs to trip at 30 by the plate markings such that the impulse takes place at top dead center or just after TDC and soon as she takes off, it's firing at 30 degrees before TDC like most engines do.

22 to 35 BTDC also works and it's not really a critical setting unless you're bent that way and can't help it, but that's a personal problem and not really a timing problem. Seeing as to how one has such a vast range to still have very good results in, most folks just set the dogs to what timing they want and then they turn the mag to impulse at 3 O'clock or a little after and call it good. It is certainly good enough. Even using a timing light is going a bit overboard then, but you can do what you want to. I will too.