wico xh mag timing????

Im having trouble timing my john deere g with the xh mag.I guess the part i don't under stand is what the process is when you pull the mag off and loosen the screws on the back of the mag how to tell what mark it sould be moved too.i have the tractor so it will run but it doesn't start as easly as it should. I have read the older posts but still haven't really comprehended it.Any help would be appreaciated.I can post pics of the back of the mag if needed.Thanks

The marks on the case are five degrees apart, the center mark represents thirteen degrees. The mark on the impulse stop disc should be to the left of the center case mark two and a half marks, that will give you about twenty five degrees lag angle. This can vary with the amount of wear in the rotor shaft and impulse plate.

Thanks for the info,i will go out and try this.The mag that is on the tractor right now does have spark, however when you rotate the mag it doesn't have a real snap to it, it just rolls over with little hesitation where there shoul be more of a snap to it.Could this be a problem?If so what should i replace?I HAVE A PARTS MAG ALSO.Thanks,Tim

Sounds like your impulse spring has broken.Should really snap when you turn it.

There MUST be a loud sharp distinct SNAP each 180 of revolution as the spring winds up and then is tripped (the spring wind n trip impulse assembly). If not theres no spark at the intial (under 250 RPM) cranking/starting although she could produce a spark at running speeds.

If theres no spring wind n trip insure the pawls (rear of mag) extend outward and engage the cup open window in order to wind the spring, if not they may be stuck corroded which a cleaning n light lube may cure. The inner spiral spring could be broken also !!!!!!!! A weak but still intact spring can cause a wimpy click or clack (and a weak spark) versus the loud sharp distinct SNAP a good spring makes when she trips.

That rear adjustments affects ONLY the start/impulse timing, its called the Lag Angle adjustment since it determines how much the start/impulse timing LAGS the advance run timing.

Its settinG DEPENDS ON WHAT DRIVE CUP YOU HAVE if you have a straight 35 degree advance drive cup then the lag angle should be set initially rough in to 35 (4 1/2 to left of top center) but if you have a straight 25 degreee drive cup it should be set to a 25 lag angle (2 1/2 to left of top center). NOTE HOWEVER, If the drive cup is labeled 6274, I believe it sets at around 4 1/4 or so to the left.

The mag should trip/impulse right at TDC for good starting and then you can adjust the run time advance by rotation of the mag in the flange, forward CW retards backwards CCW advances BUT THAT CHANGES START/IMPULSE TIMING ALSO REMEMBER so you may have to mARK THE mags position for run time advance then remove it n readjust the rear lag angle for the TDC start timing .......

At GOG Duane or I usually give a Workshop/Seminar on Wico Mags where this timing is covered in much better detail

John T

Thanks,that make more sense.i will look at the spring to see if it is broke.Are they hard to replace?THANKS

You dont really need to look at it, its hid up underneath that drive cup, if the mags removed just hold the mag in its regular upright position and turn the drive cup in the correct rotation and see if the engage pawls extend outward so the sprinG winds up then if it releases n SNAPS loud n sharp each 180. If its on the tractor crank her over (by hand if possible with plugs removed for easy cranking) n see if it SNAPS each 180 of rotation.

John T

One thing that utterly confounds me is that so many people will think they have a "timing problem" as a first thing to suspect in a magneto that is acting up. My gosh -- timing is about the LAST thing that changes - not all of a sudden anyway. Anytime folks write in with a fault or trouble question, if only they would give about three sentences with some background data - it would be ever so helpful.

For someone, based on responses received here on the board, to dig into the timing section of a defunct, worn-out magneto with this failure mode only serves to make the problem harder to solve in the long run. The first thing I'd want to know is how the tractor runs once it IS started! You say you have it "where it will run" whatever that means -- what did you do to it (if anything) to get it to run? As for starting, does it start okay when pulled? This is a very important question. If the tractor starts right up when pulled, that would pretty much point you to the impulse spring system in the maggie as the culprit.

In response to one answer telling you that you most likely have an issue with the spring, you asked if it were hard to replace! I may me wrong on this one, but if you have to ask that basic a question about your magneto, you have a choice to make, and need to make it NOW. Either take the Maggie to someone for repair, or find a video on magneto repair BEFOREHAND -- then go after it! A video by Robert's Carb is available on this site as I recall, surely in Green Magazine. And if all that fails - try the URL cited below for Robert's Carb.
Roberts Carburetor Repair Shop