1967 Mercury 500 "no spark"

[kra1956]

Good morning all, have enjoyed reading everyone's posts over the years, now it's my turn to ask for help. I have a 1967 Mercury 500 2-stroke, been running great sine Dad gave it to us 4 yrs ago. Now, no spark at all. I have replaced the points, condenser, plugs, and ohmed the plug wires, still to no avail. I'm not to educated on these motors, and could really use some direction.

Thanks

 

[GA_Boater]

Howdy and welcome to iBOATS.

On the side of the magneto is a white wire for turning the motor off. Ohm it for open when the key or switch is in run and it should be ground from the key/switch in off.

 

[kra1956]

Thanks for the reply. Without sounding ignorant, is this the same wire going into my distributor (salmon colored)? By the way, in the process of trying to find parts, I became aware that this Merc 500 has a distributor from a Merc 400 with the magneto inside if I'm correct.

 

[racerone]

Is the coil inside the magneto, yes or no ?

 

[kra1956]

Yes

 

[kra1956]

With the coil out, can someone tell me how to test it

 

[racerone]

Find a shop with a ---MERC-O-TRONIC magneto analyzer-----Coil can be tested quickly.

 

[kra1956]

Thank you

 

[kra1956]

New coil, points and condenser arrived. The new points have an insulator washer that the old set didn't have, can someone tell me the correct location for this fiber washer?

Thanks

 

[merc850]

Here's a page from the manual that will aid your repairs.The rotor should be "glued" on I use a bit of Permatex gasket shellac, this will hold it on but allow easy removal later; which you will have to do in the future to reset the points.

 

[GA_Boater]

I think the fiber washer kra has is #10 or #8. It's been too long since my magneto was torn down.

 

[kra1956]

It's a #8 GA. I have put everything back together, new points gapped, new condenser, new coil, and still can't produce a spark, quite frustrated at this point

 

[racerone]

What is your location ?------------You should be able to find a gray haired expert in your area.or take the magneto to your marine repair shop.-----Is there spark from the coil, yes or no ?---Is there spark from plug wires, yes or no ?---- -A basic mistake is being made here.----Tested the rotor ?

 

[kra1956]

Took the words right out of my mouth racerone, I feel it's something really simple (stupid) I'm overlooking, and I'm trying to locate a local "old-timer" in the Prior Lake (MN) area that can help.
coil tested good
wires ohm good
rotor ohm good

 

[kra1956]

For clarification:
coil: longer lead (primary) to points terminal, shorter lead to ground screw on base under condenser
condenser: to points terminal
ground: points terminal to magneto primary ground screw

 

[Chinewalker]

Points gapped at .008"? Have you checked for spark without fully reassembling the mag? Lay the body of the mag against a bench vice, trailer hitch, etc. Spin the magneto over clockwise with the coil tang about 3/8" away from the big chunk o' metal you're grounding the case against. Should get a good spark jumping that gap. If you have spark here, but not with cap on, then issue is with distributor portion of the equation.

 

[GA_Boater]

Check the carbon brush and spring in the center of the cap.

 

[kra1956]

No Title

Good morning, thanks to everyone for your input and expertise. The old Merc is up and running. After multiple bench tests, changed out the condenser (they sent me 3 when I ordered one?), regapped points to a tight .008 from a slip .008, and located a nearly broken ground strap from the distributor assembly to the block. Anyway, will take to the lake this weekend and run under load and final tune if needed, and of course do some fishing!

Have a great weekend everyone.

 

[kra1956]

By the way, it's a 1967 Larson All American 14ft, 50hp mercury, Wife's Dad gave it to us after owning it since 1972, sat unused for 12yrs, and we have been using it for 4, love this old boat.