Wico AP magneto

~You also really need to check to be sure the rotor disk arm is lined up with the outer cap towers as the points open for both sparks.. If the points open when the rotor disk arm isn't lined up with a wire tower in the outer cap the spark won't get to the plug.. Is the pinion gear tic mark lined up with the CCW mark on the cam? If not maybe that's your problem..

~For a thorough test you need to bend a wire [a piece old copper house wiring works good] to fit in each cap tower [you can do one at a time] then insert it in one cap tower at a time & bend to within 3/16" of the metal mag case.. Then spin the mag in the running direction & look for a bluish spark to jump that 3/16" gap.. If you don't have that bluish spark on both cap towers but do have a 3/16" bluish spark from the coil cover your problem is either the rotor disk arm not aligning with the outer cap at spark time or you have a problem with the outer cap or that little brush & spring [sometimes it helps to slightly stretch that brush spring a little.. .. I presume you have tested or tried a new secondary interlead between the top cover & the outer cap?

~Other than that verify the points open to .015" on BOTH points cam high spots..

~You could also hook a conventional coil output wire [maybe from a coil equipped tractor] to the outer caps coil input tower then install the two plug wires & plugs & lay on the engine block of the spark supplying tractor then crank the tractor in a dark location & look for sparks to arc around in the cap..

~Also make sure the brass segments on the rotor disk & outer cap are not severely pitted or burnt black..

~If the magneto doesn't pass the above 3/16" spark tests then you could have a weak magnetic rotor or a weak coil..

You also ask...

Quote: "Could it be a weak spark, strong enough to jump from the coil, but not enough to come through the first sparkplug">>>

_Yes, if the coil is weak the spark could only give you an initial spark then not make the second one strong enough to jump again.. If you get a bluish spark to jump that 3/16" test gap your coil is probably ok though..

Quote: "Is there a buildup in the coil for the second spark?">>>

_Yes there has to be a second primary charge up then collapse to get that second spark from the coil's secondary [just like the first spark]...

~If you are getting a good spark from the test copper wires on both cap towers but still no spark at the plugs suspect a fouled spark plug..

~If you are getting a spark at both plugs but the tractor isn't firing on both cylinders first suspect the mag isn't installed in the governor correctly [that Wico AP HAS to be installed correctly to get a correctly timed spark to BOTH cylinders]..You can't just reverse the plug wires like on a Wico C or X..

Any questions just post back or E-mail...

a) A problem in the cap (internal tower terminals where rotor arm passes by). Look for cracks or carbon traces or crud or any subtle differences like different distances between where the rotor tip passes by the caps inner terminal/tower points.

b) The brush or its spring or for free unrestricted inner/outer movement of the brush against the rotor arms pickup point.

c) A problem in the rotor arm.

d) There could be a rotor or cam or bushing problem. HOWEVER, IF BOTH mag snaps each produce near identical sparks out the coil wire alone, I dont think thats the problem at all.

This assumes its ONLY ONE cap terminal that has a weak spark, regardless of wire or plug swapping AND BOTH PLUGS AND BOTH wires are good.

Trying to answer your specific questions: (1)A weak spark strong enough to jump from coil but not first plug????? If the sparks real weak and there were losses in the wire and/or the plug was leaky or had a wider gap, I guess the answer would be yes. HOWEVER, if the coil wire alone is producing identically good blue (NOT faint thin wimpy yellow) on each mag snap, PLUS you have swapped plugs n wires and are SURE neither is the problem, Im back to a cap or brush problem. (2) Is there a build up in the coil for the second spark? YES theres an identical build up in the coil for BOTH sparks. However, its the same coil, points n condensor for BOTH, so if they are not equal, differences may be in the gap the points open to and maybe a problem in the rotor or cam or bushings.

MAKE DARN SURE the coil wire alone produces near identical looking sparks on each mag snap,,,,, ,,,MAKE DARN SURE BOTH plugs n BOTH wires are good by new or swapping etc.,,,,, ,,,,MAKE DARN SURE the caps inner workings in the terminal pickup areas are the same and clean n free of carbon or crud or cracks and the distances from the rotor arm to the terminal points are near the same,,,,, ,,,MAKE DARN SURE the brush n spring and that area is clean and free.

Sorry, without being there thtas about all I can think of fer now. Post back your findings and any more questions. I guess you know at idle with single barrell carbs, if you pul the left plug wire she will almost die, but if you pull the right it wont make near as much difference????? ????? ?

John T

~If you are always getting a good spark out of the top coil that means the magnetic rotor is supplying enough current to the coil to provide a spark.. That means your problem is in either the outer cap, points to rotor disk timing, or the brush in the outer cap..

~If that small spring loaded brush in the outer cap is stuck in it’s bore in a lot of cases you will get one spark but not the second spark [a common problem so check that first],,, I doubt your problem is in the rotor disk itself as that same disk provide the spark to both cap towers.. You could also have a gear timing problem so the magnetic rotor isn’t supplying the proper current when the points open on the non sparking side..

~I guess I would check that brush first, then check the outer cap for cracks or carbon tracking, then see if you can turn it with the outer cap removed to see if the spark out of the upper coil appears as the rotor disk lines up with the proper cap tower [you will probably have to use a china marker to mark the rotor disk position too see all that while turning the impulse coupling}.. If the rotor disk timing is the probelm you will have to set the gear timing..

~A last thought… Are you getting an impulse snap for both spark points? If not you have impulse problems..

Post back or E-Mail with any further questions..

JDClooney@aol.com

Am I correct in assuming its always just that ONE PLUG TOWER thats bad?? If an individual wire or plug were the cause, you can substitute/swap plugs n wires to determine if a certain plug tower out the cap is bad (as Im assuming you mean) or you have a plug wire or plug problem.

When you say you get a spark from the coil, Im also assuming thats for each mag snap as its the same coil n same points n condensor that fires each, with possible differences being in the points gap etc.

Remove the cap and inspect the inner plug terminals (where rotor arm passes by and spark jumps to towers) leadign to the external towers and look for cracks or chips or carbon or crud etc and major differences in the two. Next, insure the lil carbon brush (which contacts the rotor arm) and its spring are free to move in and out and that area is not gummed or carboned up or cracked or sticky restricting movement. Also insure the brush is not broken.

Im not sure where you might purchase a new rotor arm or brush or brush spring or an entire cap, but I believe your problem is in one of those components. If the brush n spring and rotor arm are all good, that leaves the cap and its internal tower area as a problem, maybe a crack or carbon or a bad inner terminal. Dont forget to look for cracks or carbon traces or problems or differences in that rotor arm also.

Post back or e mail jmn50@msn.com any questions.

Good Luck n God Bless

John T