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Random loss of spark

M

Muddy Rudder

New member
Hello,

I have a 1971 Johnson 125 hp outboard that loses spark when it feels like it. It seems okay for short distances (1/4 mile) but loses spark randomly when I go far (1 mile or more). It starts after a while when it wants to, nothing consistent. I think I have got it to spark a couple of times by removing a spark plug and checking the spark (may have been a coincidence). Think it is the notorious black box syndrome?

Thanks
 
take a good flashlight and look up under the flywheel for any stator insulation meltdown....black insulation drips or indication of overheating...
 
The "Pulsepack" (Battery Capacitance Discharge system) on the 1971 125hp model is powered by battery voltage. The stator under the flywheel simply provides AC voltage to a rectifier to change the battery... nothing more.

That model requires a good known battery of at least a 70 ampere hour rating. A poor or lower rated battery... OR... even a very good battery that is run down, will eventually cause damage to the "pulsepack. Bottom line... the battery and connections must be perfect!

(Voltage Drop To Battery Capacitance Discharge)
( Pulsepack 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 pulsepack. 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 pulsepack.

The diode must be installed so that the current flows from the starter terminal of the solenoid to the pulsepack... 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 pulsepack via the diode effectively eliminating the voltage drop and energizing the pulsepack with the required voltage needed for its proper operation.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:


http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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(Battery Capacitance Dischage Powerpack Test)
Various OMC Engines - 1968 to 1972)
(J. Reeves)

Purchase a small 12v bulb at your local automotive parts store (the 12v bulb is to look like a flashlight bulb, not a headlight bulb). Solder two wires to that bulb, one to the side of the bulb (ground), and the other to the positive point. You might use a bulb of a somewhat lower voltage to obtain a brighter glow... just a suggestion.

Remove the spark plugs. With the key in the on position, make sure that you have 12v going to the pack at the terminal block (purple wire). Now, connect the ground wire from the bulb to any powerhead ground. Connect the wire from the positive point of that bulb to the powerpack wire that is connected to the coil wire on the terminal board (blue wire).

Crank the engine and observe that bulb closely (CLOSELY!). If that bulb glows even the slightest bit, the powerpack is okay. It may be a very dim glow... just so it glows! If it doesn't glow, the pack has failed.

Keep in mind, that type powerpack (Battery Capacitance Discharge) demands a top notch battery of at least 70 amp hours. Any less will, in time, cause powerpack failure.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
********************
 
No signs of anything getting hot Papy, but I think Joereeves is on to something. I did have two successful trips shorter than the third where I had no trouble. The second trip when I tried to start the motor the battery was dead, it didn't have enough juice to engage the starter gear, it just spun anemically. I pulled the battery and some battery cables from my truck and took the good battery along so I could jump the battery if needed (and we needed to a few times). On the third trip I acquired a good used RV battery from a friend (seemed to start fine) and that was the day we had the random spark loss issues. Do you think I trashed he powerpack? I'll run that test you posted and install a diode to keep that from happening. Thanks for the posts guys.
 
Oh yeah, where the heck is the powerpack, I assume its the black box. I'll find out when I trace the wires. Would a failed powerpack cause intermittent spark loss or permanent?
 
On that model, it is not a powerpack, it is a pulsepack, also referred to as an amplifier. Yes, it's the black box and they have been known to be intermittent before failing completely.
 
Well, the bulb glowed. Wonder if it was just a bad battery? It turned the boat over pretty good. I did use a remote start button but that shouldn't have made any difference in whether the bulb glowed or not. Any other ideas to try?

Thanks
 
A intermittent ignition problem on that type ignition system will drive a person up the wall. Of course I always had duplicate components on hand and would simply take a short cut, install a new pulsepack, and if that cured the problem, patted myself on the back for being so brilliant in my trouble shooting procedure. :rolleyes:

That route not being available to most.... About the only thing you could do is to have your trouble shooting tools with you and when the problem raises its ugly head, check the spark as fast as possible... no spark --> pulsepack!

The above assuming that you still have the proper full voltage of 12v being applied to the pulsepack.
 
I have a running 100 hp motor of the same year that was running fine when it was taken off (been sitting a long time though). I'll throw that one on there and see if that does it. Gotta be fun working on the back of the motor in the water, I can't wait to drop a wrench or something :)
 
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