78 115HP Charging Coil failure

[aamyot]

Hi forum,

While on a recent fishing trip, my 78 115HP Johnson failed to start and I had to get a tow back to the ramp.
I checked it out at home and found weak spark on all 4 cylinders. I tested the ignition components and found problems with the charging coil.

Each side ohms out at around 285 and while cranking, only outputs 70V. The manual specs 485-635 ohms and 160V. I realize that the coil is what's causing my ignition problem, but I'm wondering if there's anything that I can do to restore my faulty coil or if I'm possibly doing it all wrong and there's another component that I should be looking at.

Whenever I've seen bad coil in other devices, they either short out, have a broken connection or just melt into a mass of goo. I'm surprised to see one with connectivity, but just lousy performance.

Any general advice on charging coils would be greatly appreciated.
Thanks.

 

[1fishbone]

Re: 78 115HP Charging Coil failure

"found weak spark on all 4 cylinders"
I doubt all 4 coils died!

 

[Joe Reeves]

Re: 78 115HP Charging Coil failure

If memory serves me correctly, the ohm reading would be approximately 630 ohms +/- 75 ohms (Someone correct that if I'm in error). I don't know why your manual would state 485 ohms BUT a reading of 285 ohms means the stator is faulty if indeed that reading is accurate.

 

[emdsapmgr]

Re: 78 115HP Charging Coil failure

Is there any chance that you were trying to crank the engine with a weak battery? The engine must crank between 250-300 rpm's to generate enough ignition voltage to start/run the engine. A weak battery may result in slow cranking rpm's and low voltage output. If you have good cranking rpm's the stator should be condemned based on the low voltage output alone.

 

[aamyot]

Re: 78 115HP Charging Coil failure

You know, I didn't meter the battery beforehand, but it had been on the float charger for at least 16 hrs. Maybe I should meter that battery and make sure my charger is doing right.

I wish this simple part wasn't so expensive. Anyone know of a alternative part # or source for second hand stators? I have seen the list of salvage companies that JB has posted. Are any of them better than the others?

 

[emdsapmgr]

Re: 78 115HP Charging Coil failure

If you come upon a dealer that sells used parts, ask about a return if the part does not meet specs/work. Most will provide an even exchange, even on used parts.