50HP Mercury - Spark ??

Mattgaw122

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How do I test for spark on a 1967 Mercury 500 50 hp outboard, it just cranks? Also it is labeled a Thunderbolt, how does this motor charge the battery. I do not see a stator under the flywheel.
Any help would be greatly appreciated.
 

GA_Boater

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I think it uses a magneto.

Is it a pull start? Got a serial number?
 

Mattgaw122

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No Title

Its is an electric start, with a serial # 2161401
 

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GA_Boater

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You do have a magneto. Disconnect the wire circled below. That is the ignition kill wire and when the key is switched off, the wire is grounded. Then check for spark. If you do not have spark, remove the 4 bolts about 45 degrees from that circle and drop the magneto. Clean the points and rotor/cap contacts. Be careful, the parts are hard to find and expensive if something gets broken. On a 500 removing the magneto can be hard because of tight clearances.


mag.PNG

I don't see a rectifier, so maybe you don't have a stator. If you do or did, there are two yellow or yellow/white wires from the stator to the rectifier.
 

Mattgaw122

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what do i do if it fires up with that kill wire disconnected? will the motor not shut off if i turn the key off?
 

Mattgaw122

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I disconnected the wire you circled and i still have no spark going to the plugs. I will drop the magneto and see whats under there.
Thanks for the advice
 

merc850

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The magneto generates its own spark so the battery is only for starting - it should stay good for a month and if you charge it every 2 weeks it will go all summer. Do not connect 12v to the circled terminal!
 

GA_Boater

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what do i do if it fires up with that kill wire disconnected? will the motor not shut off if i turn the key off?

You can pull up the manual choke or what I do is temporarily put a wire on that magneto stud and touch the wire to ground, block or any metal on the motor, to stop it.
 

Mattgaw122

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So I cleaned the rotor/cap and points back to shiny gold metal. Put back together and still no spark at all. I am at a loss with these magneto's. Any ideas?
 

Chinewalker

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You can check the spark with the mag cap and cover off. Hold the body of the mag against a bench vice or truck bumper (STEEL!) and the copper coil tab about 3/8"-1/2" away from the vice/bumper. Spin the mag over by hand and see if the sparks. If no spark, back up and recheck the points - gapped to .008"? Visually check the coil for cracks or evidence of arcing. In general, if the coils looks good, it's probably good. The only coils I've ever had to replace had issues you could see. That leaves the condenser - easy to replace if it tests bad.

Once you get spark at the coil tab, then you can assemble the cover and cap. Then place the plugs in their boots and hold them against the mag body. Spin the rotor over by hand and check for spark at the plugs.
 

GA_Boater

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Don't touch the kill wire stud when spinning the shaft. You'll get bit!

Another thing only for checking for spark, is to disconnect the condenser. If it's original, it may have shorted and that kills the spark too.
 

JDusza

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Yahoo! Ignition again!
My advice is always the same.....Get a DVM with peak hold, a DVA and the CDI Ignition troubleshooting pages.
You'll be an expert in no time and the tools woill pay for themselves on the first diagnosis as you won't be troubleshooting by parts swaps.

http://www.cdielectronics.com/troubleshootingguide/

To test spark, I use an air gap spark tester.
Good luck,
J
 

GA_Boater

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Don't need any of that fancy stuff for these magnetos. A coil, set of points, condenser and magnets. That's it. It's like fixing a lawn mower.

Also the voltages are all 20,000 volts or more.
 
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