Magneto question

jpi72 · Jan 22, 2022

I own a 37 John Deere A with a magneto ignition. I recently put a new coil and tune up kit in it. We were unable to get the tractor started by hand. We did get it started by using a belt from another tractor. The tractor ran well when it got started. The magneto sparks well off the tractor and on the bench. The impulse spring seems to be clicking ok. Not sure what to check first.

Joel

pcsaw · Jan 22, 2022

Check to see if it sparks everytime I had
one professionally rebuilt fought it for
3 years then realized it wasn't sparking
all the time ended up it was a bad coil
which was new

John T · Jan 23, 2022

Often if a tractor starts easy and runs fine IF PULL OR BELT STARTED the mags impulse spring is weak or even broken HOWEVER if it sparks
nice n strong n blue when bench tested sounds like the spring is okay. Typically the points are at fault even if oxide coated insure they are
clean bright n shiny maybe drag a dollar bill through them to buff them up and insure gap is correct...

START IMPULSE TIMING IS CTITICAL for good hand starting. If too late shes hard to start if too early she kicks back. It needs to be set to
snap/impulse right at TDC when the flywheels LHI mark passes the flat mark on side of tractor at 3 o clock CHECK START TIMING

Insure BOTH plugs are good n fresh and for a mag you should use NON RERISTOR PLUGS

John T

jpi72 · Jan 23, 2022

(quoted from post at 19:00:28 01/22/22) Check to see if it sparks everytime I had
one professionally rebuilt fought it for
3 years then realized it wasn't sparking
all the time ended up it was a bad coil
which was new

Thanks

jpi72 · Jan 23, 2022

The timing that you are referring to, is it at the back of the magneto where the prongs are at? The prongs have 35 degrees stamped in them? The spark plugs are new.
Here is a photo of us starting the tractor with the belt.
Joel

This post was edited by jpi72 on 01/23/2022 at 08:46 am.

John T · Jan 23, 2022

The marks on back of mag are for setting the Lag Angle to match the drive cup used........The Timing Marks Im talking about are LHI (Left
Hand Impulse) on the Flywheel and the flat mark at 3 o clock on side of tractor. It should snap/impulse/fire right when the Flywheels LHI
passes by the flat mark at 3 o clock (Thats TDC of left piston). To adjust loosen the mags mount bolts and rotate it CW to retard and CCW to
advance so she snaps at LHI at 3 o clock

John T

jpi72 · Jan 23, 2022

(quoted from post at 11:04:06 01/23/22) The marks on back of mag are for setting the Lag Angle to match the drive cup used........The Timing Marks Im talking about are LHI (Left
Hand Impulse) on the Flywheel and the flat mark at 3 o clock on side of tractor. It should snap/impulse/fire right when the Flywheels LHI
passes by the flat mark at 3 o clock (Thats TDC of left piston). To adjust loosen the mags mount bolts and rotate it CW to retard and CCW to
advance so she snaps at LHI at 3 o clock

John T

ok and thanks.
Joel

Magneto question

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