johnson 1972 125hp No spark??

jtwood12

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Joined
Apr 22, 2006
Messages
21
Ok I had to change a fuse, flip the wires on the selionid, but I got her cranking =). The problem no spark. I checked the the netural switch which is good or I presume, new battery, new ignition switch, dont know how to check a coil?, but the power bar across the back when the key is on I get 11.8 volts from 8 to 11 terminals. When cranking I get nothing off the blue wire from the coil. just stumped what to do and how to check it. some ideas and how to do it would be great.
 

OBJ

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Dec 27, 2002
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10,161
Re: johnson 1972 125hp No spark??

JT, here is a test procedure for the amplifier that Joe Reeves posted a while back. Try it and at least see if the amp is good.<br /><br />If the amp tests' good, give a look at the points under the flywheel. May need reset.<br /><br />Here's the test procedure.<br /><br />(Battery Capacitance Dischage Powerpack Test)<br />Various OMC Engines - 1968 to 1972)<br />(J. Reeves)<br /><br />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.<br /><br />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). <br /><br />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. <br /><br />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.
 

jtwood12

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Joined
Apr 22, 2006
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Re: johnson 1972 125hp No spark??

Can you give me a run down on the order of things the motor goes threw to get spark? I.e. battery, coil, pp, stator, etc. etc. from first to last. thank you. oh almost forgot i need to re wire up the rectifier I un hooked it with out marking it now have no clue thanks again
 

marysboats

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Apr 25, 2006
Messages
52
Re: johnson 1972 125hp No spark??

The 72, 125 use's a sensor, not point's. It has a anti-reverse spring around the crankshaft, and under the ignition stator plate. If worn in two, it will short out the ignition. It has a clipper assembly wired into the ignition, it could be blown. There should be a cover over the wiring panel. There is a wiring diagram on this cover. You need a peak reading volt meter to get a reading at the blue wire, or a test bulb as explained above.
 

jtwood12

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Joined
Apr 22, 2006
Messages
21
Re: johnson 1972 125hp No spark??

Ok heres the update, Iget light at the blue bulb. but still no spark. I am trying to take off the flywheel but seem to be having problems with holding it while I try to get the upper nut off. I will update when I get it off. Thanks again guys for the help
 

ezeke

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Sep 19, 2003
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12,532
Re: johnson 1972 125hp No spark??

Rectifier to Terminal Block 1972 125:<br /><br />Rectifier Yellow to 2;<br />Rectifier Red to 6 [+12 volts from battery];<br />Rectifier Yellow and Grey to 4. <br />Rectifier Black to Ground on powerhead.<br /><br />Some rectifiers have two solid yellow, still 2 &4.<br />Some rectifiers have no black ground wire - grounded through metal case anyway.<br /><br />Tach lead grey to 4.
 

jtwood12

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Joined
Apr 22, 2006
Messages
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Re: johnson 1972 125hp No spark??

Great thanks guys. I got her to fire today and will be hitting some water this weekend to make sure lower unit is fine with shifting and such. Greatful for you help thank you.
 

jtwood12

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Joined
Apr 22, 2006
Messages
21
Re: johnson 1972 125hp No spark??

Wait its back Ok A week ago or so I stated there was no spark, then there was spark and every thing ran fine. Well there is no spark again, I tested the PulsePack with the light before it glowed now it does not. I ran the motor 2 times it ran fine. I havent done anything to it aside from change the lower unit oil. Does this motor have a sensor in the lower unit which willnot allow it to run if persay the oil is low? just realy starting to not want this boat anymore due to the one day it works the next it does not. any help would be awesome thank you.
 
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