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1972 Johnson 100hp just stops dead

D

Dave Nichols

Guest
" My 1972 100hp Johnson V-4 ru

" My 1972 100hp Johnson V-4 runs great after I launch the boat - just humming along - smooth as silk. Then it just cuts out without any symtoms -just dies. Goes from 3000 rpm to nothing lickity split - gets real quite, real fast. I hear the prop coast to a stop and the water wave catches up and washes into the back of the boat. I wait 5 minutes it starts but runs rough - if I sqeeze the bulb it seems to help at this point - but eventually it just cuts out and leaves me waiting to go again. Help - salmon season is coming up and I need my boat! Thx. "
 
"Dave.... If the engine cut ou

"Dave.... If the engine cut out by dying down gradually, it would be a fuel problem. If it simply died down like you turned the key off, that's an ignition problem.

It sounds like you have a intermitent powerpack problem which will eventually fail completely. Unfortunately, the only way you can test that type powerpack is if it does fail and stays failed while you do the test which I have outlined below.

Should you fine that your powerpack is faulty, I do have one new improved OMC pack left in my remaining stock.

(Battery Capacitance Dischage Powerpack Test)
Various OMC Engines - 1968 to 1972)

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.

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.

Joe
"
 
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