1968 Merc 200 20hp stops missing when disconnect top spark plug

[charly1954]

My 68 Merc started missing a month ago, its seems to be getting worse each time I go out. Both plugs have spark but I changed them anyway and replace fuel line from tank to engine. Didn't replace the ball hand pump.

Trying to avoid having to pop the flywheel off I did one last test, Pulled one plug at a time and started it. When I pulled the top plug(running on just bottom cylinder) there was no missing. Then I pulled the bottom plug and started it, it started missing. So I.m thinking I probably have a bad top cylinder coil, points, or condenser. Before I pop the flywheel was wanting some advice.
tks

 

[tommarvin]

charly1954, you solved the problem.
You did a cylinder drop down test,
When you pulled the top plug wire and running on the bottom cylinder only,there was no missing.
Then you pulled the bottom plug wire and the top cylinder started missing.
You need to remove the flywheel ,clean everything and test the coil points, and condenser, if you dont want to test you can buy new parts.
You tube will have video on how to test your parts, probably just a multi meter is needed,cleaning and adjusting the points may do it ,you got this.

 

[Chinewalker]

Those Phelon condensers are typically the weak spot in an otherwise sturdy magneto. New ones are available - replace both, as the other is likely to give you issues down the line. Save it, though, as it may come in handy during future troubleshooting...

 

[charly1954]

tks for the replies, appreciated. Getting ready to "try" to pull the flywheel, I know from the past it doesn't come off easy so I have to be patient.

1968 OEM Parts are hard to find, this site shows my points(398-2320) and condenser(398-2203) are unavailable. I found them on marineengine online but outrageous prices(1 points $50, 1 condenser $36). Anyone know of a site that sells aftermarket parts I may need a little less costly.

 

[racerone]

Finding a parts motor could be a good option.

 

[charly1954]

Pulled the flywheel tested the coils and results does not make sense.

Tested both coils with meter and the ohms droped to 0 when I probed ground wire and wire to points. But when I tested both coils ground and spark plug wire end the meter did not move. Which I believes means both coils are bad. That's the part that makes no sense because the lower cylinder ran with no missing when top wire pulled and the top missed when the lower wire was pulled.
The coils where on the motor for testing, also got same results after I pulled the stator assembly of the motor. I couldn't get the coils off to actually test the spark plug coil terminal. There are flat spring clips on both sides off the coil and I didn't want to pry to hard to pull them off. I looked all over the net and youtube and could not find how to pull the clips. From memory I am thinking the 2 clips interlock and the outside clip is supposed to pull out first so the coil will slide off the magneto.

All in all I am puzzled why the "ground to spark plug" test on both coils read bad when the motor ran(only top cylinder missed) right before testing.

 

[charly1954]

Tried to edited and add to last post but edit icon is missing, anyone know why.

As I said in previous reply I tested both coils and could not get a good reading on both coils(ground to spark plug). So I cleaned points with sand paper and put stator and flywheel back on. It was dark by then so I wraped a rope around the flywheel to test for spark, had spark on both plugs which surprised me.

 

[GA_Boater]

Tried to edited and add to last post but edit icon is missing, anyone know why.

As I said in previous reply I tested both coils and could not get a good reading on both coils(ground to spark plug). So I cleaned points with sand paper and put stator and flywheel back on. It was dark by then so I wraped a rope around the flywheel to test for spark, had spark on both plugs which surprised me.

You only have period of time to edit a post. 8 hours after posting is too long.