Help - Mercury 500 - no spark!

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Somethingfishy
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Help - Mercury 500 - no spark!

Post by Somethingfishy »

Hi all, On a broom Saturn, I have a mercury 500 (50hp) of circa 1972 vintage but running later (circa 1979) electronics. Having had her running fine on 8th May, I now, 2 weeks later, cannot get her to start and it appears that there is no spark reaching any of the plugs - I am stumped as to what to do so any advice greatly received as the electronic unit looks sealed, and beyond my capabilities of repair! On removal of the top coal, There is also a small plastic block where the cable was so corroded it crumbled off (pictures) what’s the purpose of this switch and where could I get another?
Any advice of diagnosing the lack of spark or what this component is is much appreciated! Thanks in advance Andrew
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Rapier
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Re: Help - Mercury 500 - no spark!

Post by Rapier »

Crumbling wiring is a typical Mercury problem... It looks like the mercury switch - readily available online ( if not, from Duncan Walker, or try Burseldon Outboards). It's a bead of mercury that interrupts ignition if you hit an underwater obstruction that kicks the motor up beyonf a prescribed angle. OMC motors didn't have it - there was a great Mercury promo film with an Evinrude that had torn off a transom upon hitting a log and was about to chew the driver up.
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floater
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Re: Help - Mercury 500 - no spark!

Post by floater »

I'd say, and am fully prepared to be proven wrong that the fact that the wire to the mercury switch is disconnected is not the cause of the problem. When the engine tilts the mercury flows and makes a circuit that shorts the ignition and stops the motor. This will not happen With the wire disconnected. Even if you are trying to start the motor tilted up it should still spark because the mercury switch is disconnected.

As Rapier says the original wiring is rubber coated and crumbles, my 1980 motor had suffered this extensively to the extent that I fitted a new stator and trigger and rewired everything else.

I would start with the control box and check the kill switch and start in gear switch. Also the connection between the control box cable and motor.

Good luck

Somethingfishy
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Re: Help - Mercury 500 - no spark!

Post by Somethingfishy »

Thanks for your responses Rapier and Floater. Will get a replacement mercury switch and look to trace from the remotes back.

Somethingfishy
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Re: Help - Mercury 500 - no spark!

Post by Somethingfishy »

Having sort advice on how to test, it seems as if I can rule out the mercury switch and now the remote and kill cord switch from the issue so looking more likely to be the stator or cdi unit. Any advice on how to remove the flywheel and test stator, or indeed test the cdi unit or (god forbid, advice on where to purchase a new one?!)
This maybe getting beyond my capabilities now!

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Rapier
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Re: Help - Mercury 500 - no spark!

Post by Rapier »

No need to remove the flywheel until you know the stator's u/s and the switchbox is easy to replace if that's the problem - I may have a spare, but will check tomorrow. Where are you based? I also have a Mercury / Mariner diagnostic 'suitcase' and the specs for the 500 ADI ignition motor.
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floater
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Re: Help - Mercury 500 - no spark!

Post by floater »

I was just typing a reply but Rapier has beaten me to it

Flywheel puller here
https://www.ebay.co.uk/itm/Flywheel-Pul ... SwdIVeZgg9

But as Rapier says you don't need to remove it to test the stator, there's details on how to test it here on pages 89 and 100
http://www.cdielectronics.com/wp-conten ... igital.pdf

To test the switch box as Rapier says requires the special Mercury test kit.

New stators and switch boxes are available from Sierra who's UK agent is Keypart but you need deep pockets I'm affraid. Mine came from Mercury agent Duncan Walker at Reading

Sierra catalogue here-
https://www.marineengine.com/parts/sier ... talog/364/

Somethingfishy
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Re: Help - Mercury 500 - no spark!

Post by Somethingfishy »

Thanks Rapier and Floater. I am actually based in Stratford-upon-Avon, Warwickshire but she’s on a good trailer so happy to travel wherever to help get it diagnosed.
if your able to help with the special kit that would be very kind, as I’m stumped and itching to get to the club hamble rally on 19th/20th!

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