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72 Johnson 50 hp wont start...how do I

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72 Johnson 50 hp wont start...how do I

Old 08-18-2011, 04:50 PM
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Default 72 Johnson 50 hp wont start...how do I

Hey everyone. I'm new at working on outboards, so I'm lost.
My 72 Johnson 50 was running good, now wont start. I was running on water hose and shifted into forward giving it a little throttle (I know, I know...was testing a tach)
Slowly shifted back into neutral and it died and hasn't started since. I put new plugs in, it had a new stator already. I don't know how to test stator and powerpack, but have a volt/ohm meter if someone could walk me thru it. I did unplug the big yellow fuselink? and tried to start by jumping with cables to starter thinking it might be neutral safety switch, but no luck. HELP!!
Thanks in advance for any help. I know I need a service manual...it's on the way! Can't just sit around and wait on the mail and not try something.

Last edited by tidefisher; 08-18-2011 at 04:58 PM. Reason: left ou info
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Old 08-18-2011, 05:00 PM
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Just something to get you started until the experts jump in. If the neutral switch is the culprit, the engine will not crank at all. If the kill switch is the problem, the engine will crank but the ignition coil will be grounded so you will get no spark to the plugs. Find out if the engine cranks. If it does, remove a spark plug and see if a spark is present when cranking. Also, see if the plug smells like gas.
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Old 08-18-2011, 05:05 PM
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getting blue spark at plugs, and took 7/16 screw out of bottom front of both carbs...fuel leaked out so I assume carbs are getting fuel and plugs do smell like fuel. Compression is 100 and 105
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Old 08-18-2011, 05:22 PM
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Ok, you need four things to make an engine run. Fuel, air, compression and a spark AT THE RIGHT TIME. You seem to have fuel and compression. Time to look at the other two. Thats all I've got right now.
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Old 08-18-2011, 05:45 PM
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blue spark is as normal with yellow plug connected and starting with switch
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Old 08-18-2011, 05:46 PM
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should I try iand see if I have same spark by cranking with cables?
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Old 08-18-2011, 06:46 PM
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ok experts-jump in here anytime...please
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Old 08-18-2011, 06:47 PM
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thanks Uncle John
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Old 08-19-2011, 08:44 AM
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no help here...maybe I should try iboats forum
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Old 08-19-2011, 09:29 AM
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Just traded in a Johnson 48SPL which is pretty much the same motor I believe.

I had a no start problem which turned out to be the floats in both carbs. I took off the airbox and squirted fuel into the carbs and it started right up but ran rough. When I rebuilt the carbs it started right up but then idled rough. I changed the plugs but that didn't help. Eventually I found a kink in the fuel line just under the starter motor, so I rerouted the fuel line to have the shortest distance to the pump and that cured the rough idle.

My compression was 120 in both cylinders so I think yours is kind of low as I think mine should have been around 130-140.
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Old 08-19-2011, 03:55 PM
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Originally Posted by tidefisher View Post
blue spark is as normal with yellow plug connected and starting with switch
You can't test spark by using a sparkplug, it has to jump a 7/16th inch gap to prove its generating 30K volts or it will not spark under compression.
Thats a mistake most newbies make trying to diagnose outboards.
Go to the auto store and get an adjustable gap spark tester, they're very cheap.
You need to see a bright blue SNAP!
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Old 08-19-2011, 06:22 PM
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Thanks for the tip jonesg. I first tried the blue spark at plug technique, then I got an inline spark tester...I saw a spark at the bulb, but it was faint in the daylight...nothing like the light from the same tester on an automobile. An old outboard mechanic told me to get a known good plug and remove the ground electrode and try the blue spark/snap test. I did and no spark. Even more confused now.
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Old 08-20-2011, 11:52 AM
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Inspect the coils, if they're cracked they are finished.
I'd just replace them if they're original.
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