1972 Johnson 50 Hp Intermittent Spark No Spark

I have a 1972 50ES72C Johnson 2-Stroke that died on cold startup and I now cannot get running. It was running okay a few days before.

I replaced the spark plugs because I could have fouled them.
No start.
I inspected/ohmed the coilpacks and replaced them with new OMC coilpacks. (Both new OMC secondary wires ohm out the same at 2100 ohms)
No start.
I disconnected the Black/Yellow kill switch wire from the powerpack.
No start.

The battery is charged to 12.8 volts.

When I test for spark with the new coils, I have no spark on cylinder one.
When I tested for spark with the old coils, I had no spark on cylinder two.
When I was testing the old coil, a switch of the primary lead at the powerpack between both cylinder one and the cylinder two lead, both powerpack leads sparked. (The old coil ohmed out at 270 ohms)
Lastly I installed two new OMC 0502890 coil kits, they both ohm at 2100 ohms on the motor, and now only cylinder two has spark.

I stopped there and ordered a repair manual, but would someone have experience with why the spark intermittently doesn't spark on cylinder two, and then, after installing new coil packs, has no spark on cylinder one?

I want to swap primary wires again, but both coilpacks are new and spec the same. My wrist is starting to beef up from taking the powerpack cover on and off with those flatheads.

Stop swapping wires around.-----I would take starter apart for inspection and ohm check on armature.-----Costs nothing to do that.------If starter is good , install a new powerpack.-----That fixes it 9 out of 10 times.

racerone said:

I would take starter apart for inspection and ohm check on armature.-----Costs nothing to do that.

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The starter has not had a problem to my knowledge. It engages, disengages, and turns the engine over well. Am I missing something with the check; I am inspecting the armature for loss in rpms at cranking?

racerone said:

Stop swapping wires around.

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Thank you for the reply. I should clarify that I had both boots disconnected from the cylinders/plugs at the time of testing spark, but having the plug trying to fire on the wrong cylinder, that would be bad, yeah NEVER do that.

racerone said:

install a new powerpack. ----- That fixes it 9 out of 10 times.

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Ok. For clarification and confirmation. If I have one old coilpack that could show spark from either primary post, but two brand new coilpacks made the dead cylinder swap from bottom to top; the powerpack is suspect?


Forgive my asking a second time. Are these ignition modules rpm related, and will the stator or timing sensor have their say in ignition here? As instructed, I am taking a break from wire swapping and hunting, until I can get schooled some.

Some love to argue.-----Flywheel needs to spin fast in order to make spark.----And 12 volts from battery is not used to make spark on this system.----The fast spinning flywheel generates the spark.-----Since I can not see or hear your motor you need to do inspection ---Sorry.

racerone said:

Some love to argue.-----Flywheel needs to spin fast in order to make spark.----And 12 volts from battery is not used to make spark on this system.----The fast spinning flywheel generates the spark.-----Since I can not see or hear your motor you need to do inspection ---Sorry.

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Ok. Am I looking for burnt windings? Or are there varnished brushes, anything specific to notice when taking the starter apart?

I'd like to post back.

The following probably contains my answer, but if anyone has insight, please let me know.

CDI Troubleshooting Guide below.

NO SPARK ON EITHER CYLINDER:

1. Disconnect the black yellow stop wire and retest. If the engine's ignition has spark, the stop circuit has a fault-check the key switch, harness and shift switch.

2. Check the stator resistance. You should read approximately 500 ohms from the brown wire to engine ground.

3. Check the DVA output from the stator. You should have a reading of at least 150V or more from the brown wire to engine ground (while connected to the pack).

4. Check the timer base?s resistance from the black/white wire to the white/black wire. Reading should be 10-20 ohms (or 30-40 ohms for CDI Electronics 133-0875K1). Note: The original factory specifications was 8-14 ohms, this was changed around the mid 1970?s in response to the change in SCR?s triggering requirements.

5. Check the DVA output from the timer base. A reading of at least 0.5V or more from the black/white wire to the white/black (while connected to the pack) is needed to fire the pack. If the output is low, you may try to reset the air gap between the timer base sensor and the triggering magnet.
a. Loosen the two mounting screws on the sensor and the nut located in the epoxy on the outside of the heat shield of the timer base.
b. Slide the sensor in toward the crankshaft approximately 0.005? at a time.
c. Coat the face of the sensor with machinists bluing or equivalent.
d. Install the flywheel according to the service manual and crank the engine over.
e. Remove the flywheel and check to see if the trigging magnet struck the sensor face.
f. If the ignition fired, finger tight the nut on the outside of the heat shield and coat it with RTV.
g. If still no fire, slide the sensor in another 0.005? and repeat steps c through f.

6. Check the DVA voltage on each trigger wire to engine ground. You should have a reading of at least 150V or more from the black/white wire and the white/black wire to engine ground (while connected to the pack). If the reading is low, disconnect the trigger wires from the pack and recheck the terminals on the pack. If the voltage jumps up to an acceptable reading, the timer base may have a problem in it?s internal wiring (A thin spot in the insulation on one wire).

7. Check the cranking RPM. A cranking speed of less than 250-RPM will not allow the system to spark properly.