1972 johnson 100hp no spark while cranking over..

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skidoo16x

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hey guys i have a 72 johnson 100ho, the engine does not have spark while under full cranking power, when you let off the key after cranking the motor will spark 2 or 3 times?? any info on this or any ideas would be greatly appreciated!





thanks keith
 
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emdsapmgr

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Re: 1972 johnson 100hp no spark while cranking over..

Could be a short in the key switch. Disconnect the control box harness at the engine. Try jumping the starter with a known good battery. If you have spark, the problem may lie in the contol box/control box harness.
 
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F_R

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Re: 1972 johnson 100hp no spark while cranking over..

Check the voltage on terminals 8 & 9 (purple wires) on the terminal strip on the back of the powerhead while cranking. Sorry, I don't remember what it must be, probably at least 10.5 or 11 volts?? If low, check the battery (have it load tested). Also check all battery cable connections and the cables themselves. Don't just look at the connections, take them apart and clean them shiny bright and make sure you reinstall them tightly. Could be the key switch too.

Terminal 9 is the input to the pulse pack.
 
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boobie

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Re: 1972 johnson 100hp no spark while cranking over..

Are the spark plugs in or out when checking the spark ?? Sounds like you have low voltage going to the power pack when cranking.
 
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skidoo16x

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Re: 1972 johnson 100hp no spark while cranking over..

thanks guys i actually found i had a(brand new) fualty ignition.. so i got the motor started it hasnt run in a long time now i just gotta tune it up doesnt want to idle.
 
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skidoo16x

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Re: 1972 johnson 100hp no spark while cranking over..

have another question now, what are the carb settings for this motor it wont idle
 
halfmoa

halfmoa

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Re: 1972 johnson 100hp no spark while cranking over..

A carb rebuild is in order before you start adjusting them especially considering that it's sat for a while.
 
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F_R

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Re: 1972 johnson 100hp no spark while cranking over..

skidoo16x said:
have another question now, what are the carb settings for this motor it wont idle
Click to expand...

There are no adjustments on those carburetors. Everything is fixed jets. The idle jets are one on each side, behind the screws, below/fwd of the throttle shafts.

The screw heads in the silencer are just plugs, to be screwed in tightly.
 
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emdsapmgr

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Re: 1972 johnson 100hp no spark while cranking over..

If the idle is set too low, you can raise the rpm's by screwing in the large screw on the spark advance lever. That engine should be set to idle between 650 and 750 rpm's, set when the boat is floating in the water and it is in forward gear. You can't set it on the trailer. If it's not just a simple idle screw problem, then follow halfmoa's suggestion.
 
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