1972 Johnson 100 HP Ignition Trouble

[General66]

Hello, this is my first post here as I'm new to the forum. Therefore, I apologize if I miss a critical 'must-do' for posting. I've searched through a lot of posts and I've gotten some good techniques for testing the ignition on my motor, but I'm now at a point where I need some guidance of what to do next. First, as stated in the post title, I have a 1972 Johnson 100 HP outboard that is having some ignition issues. I winterized the boat last fall without issue, but trying to start it for this season has proven to be a headache. I don't have spark at any cylinder and I don't have spark from the ignition coil. I've tested this using a spark test light and a spark gap tester set for 3/8" to 1/2" per manual specs. Last year I replaced the original ignition coil with a newer one from Sierra Marine (part number 18-5193). Following replacement, the engine did run up until winterizing. With the no spark issue, I've followed the CDI manual for troubleshooting along with an older version of the almost same instructions (I forget the source...). I've got an older power pack/clipper circuit setup that I've tested. I have performed voltage drop testing on the battery cables and starter system to see if I've got significant drop, and I'm dropping about 0.5-0.6 V along the older battery cables. I will be replacing these in the near future. I am getting at least 9.5 V to the purple lead of the power pack, and I'm also getting 255 V of DVA measured output from the output lead to the ignition coil, so according to what I've read, the power pack should be OK. Therefore, I've done some resistance testing of the ignition coil to see if anything stands out, and the readings I've acquired are 0 Ohms for the primary winding and 275 Ohms for the secondary winding. According to the original shop manual, it states that the primary winding should not exceed 1.3 Ohms, and the secondary winding should not exceed 3000 Ohms. This is based on using some specific tester listed in the manual. From what I've read elsewhere, and not knowing where to find the specs of the Sierra coil unit, you should at least have a few tenths of resistance in the primary winding. I'm not sure of what the correct specs are for the secondary winding either. So, following this novel of explanation, I'm at a point where I need some assistance. Does anyone know what the resistance specs should be on these aftermarket coils? I haven't seen any specs listed throughout any search I've run here. Since I have zero resistance on the primary winding, do I have a bad coil? Also, one additional question. If I'm reading 255 V or so from the power pack output lead, can I assume that the sensor assembly is good? Thank you ahead of time for any help with this issue.

 

[Joe Reeves]

Gentle Hint..... Best to use short paragraphs, those long one paragraph explanations result in hard reading for some of us older fellows.

Having worked an many of those engines back when they were new, I and many others have learned a few things. You've, however, covered much of the bases already.

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(Clipper Circuit)
(J. Reeves

OMC issued a bulletin many years ago pertaining to that Clipper Circuit. It was originally designed to protect the pulse-pack from voltage surges caused by the charging system. As it turns out however, it caused more problems than it cured. The bulletin stated to remove it completely, then to run the 12v supply wire that normally ran to the Clipper Circuit (12 volts active only when the key is in the ON or START position) directly to the Pulse-pack voltage supply terminal.
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Pertaining to the missing coil readings... sometimes this happens simply because the ohm meter is set wrong, needing to be set to a higher reading... and most of the time, it isn't the actual resistance reading we're interested in. What we're interested in is the continuity (as follows)... and if that is missing, replace the coil.

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(Battery Capacitance Discharge Coils - Continuity Test)
(Joe Reeves)

Remove the primary wire the screw type terminal. Remove the coil and unscrew the HT wire from the distributor cap.

Connect the black lead of a ohm meter to the HT wire, then with the red ohm meter lead, touch the ground wire of the coil.

Then touch (still with the red lead) the wire that normally attaches to the powerpack output lead. You should get a reading on both touches (contacts). If not, check the HT wire by unscrewing it from the coil. After removing the wire, the check can be repeated using the internal threaded prong within the coil instead of the HT wire. Poor or no continuity of a coil is one reason for erratic or no ignition and/or s/plug fouling.
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Now, That type of ignition (Battery Capacitance Discharge) demands a top notch fully charged battery of at least 75 amp hours of which I'm sure you're well aware... BUT... as the engine ages, the starter begins to draw a bigger share of amperage, and this results in a loss of power/voltage to the pulse-pack. The cure to that is as follows:

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(Voltage Drop To Battery Capacitance Discharge)
( Pulse-pack When Electric Starter Is Engaged)
(J. Reeves)

On the older Battery Capacitance Discharge ignition systems (1968-1972), the electric starter reaches a point, even with a top notch battery, whereas the starter will draw excess voltage/current/whatever which results in a voltage drop to the pulse-pack. The cure is to purchase a diode which is capable of handling 12 volts and installing it between the starter terminal of the starter solenoid (NOT the battery cable terminal) and the wiring terminal that supplies voltage to the pulse-pack.

The diode must be installed so that the current flows from the starter terminal of the solenoid to the pulse-pack... NOT vice versa. When that diode is installed in this manner, when the key is turned to the start position, the voltage that is applied to the starter is also applied directly to the pulse-pack via the diode effectively eliminating the voltage drop and energizing the pulse-pack with the required voltage needed for its proper operation.
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[General66]

Hi Joe,

Noted on the smaller paragraphs...

I've read all of your attached suggestions in many other posts, and I thank you for them! I have a couple of questions regarding clarification for my understanding.

For the clipper circuit, I can simply remove it? If I understand the wiring diagram correctly, the 12V is supplied at terminal 9 via the purple wire and the clipper circuit is connected there, too. So you're saying just remove the clipper circuit lead from terminal 9 and simply have the two purple leads left, one for the pulse pack and one for the thermo switch?

For the coil readings, my multimeter has auto ranging. The way I tested, since it's the newer coil with the spark plug boot HT lead, was by simply touching blue input lead to black ground from coil (for primary), and then the same with the HT post, where the boot attaches to, to the black ground of the coil (for secondary). All this was done with the coil removed. Does that cover the same bases as what you suggest?

For the pulse pack with the starter engaged reference, if I'm getting the 255 V DVA reading, can I assume that the pulse pack is working properly? As for the diode, I know you stated in another post that it should be the size of half a peanut shell or the like. Not the small ones. Any pics of something to go by?

Thanks, again!

 

[General66]

Can someone confirm that if I'm seeing 250+V from the pulse pack that it should be considered good? If so can I assume the timing sensor is good? If not, does someone know the resistance specs of the timing sensor?

 

[General66]

Well, it turns out that if you're seeing any sort of voltage from the power (pulse) pack over 200V, they it's good. I was able to get my outboard started, and it looks like it may have been a simple (I use that word loosely) grounding issue. My coil tested fine for continuity; therefore, I reinstalled it, but I placed the grounding wire in a different location. I grouped it together with the long ground lead from the pulse pack. Following reinstallation, I had good spark and she turned right over perfectly. The only things I did to change from a no spark to good spark issue is slightly clean/scrape the ground contacts of the pulse pack, and also relocating the coil ground lead.

One quick question regarding cleaning of ground connections. Should I use emery paper, or a wire brush and then add dielectric grease to the terminals prior to reinstallation?

I guess two questions... I have a copy of the original shop manual for an Evinrude 1972 100 HP Starflite outboard. Will this be exactly the same as the 100 HP Johnson outboard (100ESL72R) or should I get a manual for the Johnson specifically?