1971 40hp - No Spark at plugs

bhgran

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Nov 13, 2009
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2
I have obtained a 1971 Johnson seahorse 40hp motor. I replaced the plugs and cannot get any spark to them when turning the motor over. I pulled the flywheel and the top end looks good, no corrosion or anything that "looks" out of place.

Where do I start in diagnosing this problem??? Any and all advice would be greatly appreciated!!
 

bktheking

Vice Admiral
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Jul 29, 2008
Messages
5,057
Re: 1971 40hp - No Spark at plugs

Clean and adjust the points to .020 for starters. Is this a rope start or electric start model?
 

KB1

Seaman
Joined
Jan 2, 2006
Messages
50
Re: 1971 40hp - No Spark at plugs

Evenin'

Had one up 'til May. Good motor.

Elec. start w/ key? Make sure ig. is on.

Flywheel torqued back to 105 ft. lbs.? Better be.

If control cable equipped, is the throtttle control too far advanced? (check on starboard side of engine and make sure the plate under the flywheel is not contacting the safety switch. If it is, it will do nothing until you back off the throttle. No click. No nothing. Same situation if the tiller handle is twisted too far.)

Check and holler back.
 

bhgran

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Nov 13, 2009
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Re: 1971 40hp - No Spark at plugs

Sorry for the lack of info....
It is an electic start w/key. the flywheel did get re-torqued.

I do have cable controls on this engine, but still didn't get any spark when adjusting the throttle lever back towards idle position.

Electric choke works, and the compression is good on the motor. Motor turns over well, with new battery.

I am missing something?
 

bktheking

Vice Admiral
Joined
Jul 29, 2008
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5,057
Re: 1971 40hp - No Spark at plugs

I am missing something?

Yes a couple of things :D

I only have the wiring back to 73 but the components look similar.

There are 3 wires going to the magneto, please confirm.

First, you have a fused wire in the diagram going from the ignition switch to the magneto, check it.

Second, there is a kill switch or shorting switch I think they call it going to the magneto, it is a grounding switch, disconnect it (2 wiring harnesses, one from each side of the switch) and test.

Third, the magneto has a wire going to ground, make sure it is clean and grounded.

And of course what I suggested to begin with , clean and adjust points if they need it.


Playing with shift levers to re engage switches has zero to do with spark, one would assume that being an electric start and you have verified you have no spark that the neutral safety system is working. All this does is provide ground to the other terminal of the solenoid. This is either a bad coil(s), dirty or bad points/condensers or something in the wiring/ignition swich.
 

KB1

Seaman
Joined
Jan 2, 2006
Messages
50
Re: 1971 40hp - No Spark at plugs

I agree w/ bktheking. The shift levers have nothing to do w/ the electricals.
The throttle lever does. Check it out. If that switch is bad, then its bad.
 
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