IH H4 Magneto Questions--I need help!

My H4 Magneto will only give off a weak yellow spark, not enough to fire a sparkplug. I have tried to attach two pictures showing what I am doing to test the coil. I am trying to determine if the coil is bad. It has new points, condenser, cap and rotor and the rotor seems well magnetized. Is my coil really bad?

Second Photo showing resistance on 20 ohm scale.

I can't get the second photo to come up. Anyway, it shows a resistance of 1.2 ohms on the 20 ohm scale.

I'm NOT sure what a typical primary resistance should be, but 1.2 Ohms sounds pretty low.

On the other hand, there's really no accurate way to completely test a coil with an Ohmmeter, 'cuz even ONE shorted turn in the windings will greatly reduce spark output (turning the energy into heat in the coil).

Those coils COMMONLY partially fail, and since you've pretty much covered the other possibilities, I'd replace the coil.



http://www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-5035%20Service%20Manual%20Magnetos/index.html
Blue Ribbon Mag Service Manual

I agree, not a good way to test them with an ohm meter. That reading is about right though on the primary. I think the secondary reading should be about 7000 to 9000 ohms. I have it wrote down out in the garage some where. I have a Graham coil tester but the problem with a tester is having the specs for each and every coil. If your impulse is working good, known good condenser and points you pretty much have to go with coil.

Check your magnets for magnetism using a flat blade screwdriver. I would replace the coil too.
Hal

Usually the primary doesn't go bad but the secondary will. If the secondary is open, pitch it. If closed, get it tested.

Pappy, heres the deal:

1) A low voltage ohm meter continuity test can tell you if a magneto coil is definitely BAD, such as an open circuit. If EITHER the LV primary or the HV secondary fail a simple continuity test, THE COIL IS BAD

2) HOWEVER just because BOTH the LV Primary and HV secondary are continuous and within the correct ohms range, THE COIL CAN STILL BE BAD as many coil breakdowns are due to HV breakdown especially once all warmed up WHICH THE LOW ENERGY LOW TEMPERATURE LOW VOLTAGE OHM METER TEST WILL NOT INDICATE.

3) Typical mag coil LV primary resistances are often quite low, say 0.5 ohms to under 2 ohms, while the HV Secondary is often several thousand ohms. Don't have a calf anyone, there are a lot of mags and a lot of mag coils and different resistance values so this isn't true for alllllllll freakin mags

If the coil doesn't pass the smell test or looks like its been hot, it may be bad even if it passes both LV and HV continuity.

More typical problems are the points or points adjustment or the condenser or the rotor has lost magnetic strength, but if that's all good??? sure its possible a coil is bad even if the ohm meter shows both windings are continuous and within the correct resistance range.

Its NOT GOOD to dry fire a Mag with no spark plug etc on the HV output cuz the voltage rises to higher then normal levels and may cause an arc or short in the HV windings with HV breakdown thereafter.

If a mag produces a hot spark when running or pull started but NOT when shes cranking, the impulse mechanism may be weak even if the coil and points and condenser are all good.

Got it???

John T NOTE I have gave Seminar Workshops on Wico Mags but Im NOT an IHC Mag man so no warranty

I forgot, my bad, the spark is weaker if theres no condenser ya know!!! Although sure they still fire with no condenser at all but will NOT fire if the condenser is shorted out WELL DUHHHHHHH

John T

Thanks everyone. The coil looks like it has been hot. This clears up my suspicions. Coils are not cheap, but looks like I will be looking for one. This mag is an extra one but I like to have one on hand just in case.