Mag gremlins.

[geoffwga1]

OK here's the deal. I have been plagued for a long time with intermittent loss of spark on one cylinder of my 73 40hp Norseman. I have stripped the mag down to it;s basic components.I have changed the coils,the points the condensers,the high tension wires and just about everything else.Disconnected the kill wires and timed the points gap using Frank's gadget.If I had any hair left I'd be tearing it out so if anyone has any constructive ideas I'd love to hear them.This may be one for Racer,he's just about seen it all. Just am
n aside,I've stripped and rebuilt dozens of these pretty simple devices but this one has got me beat, HELP.

 

[Crosbyman]

do you loose it solid like and it gets back normal after a cool down period ?.
have condensers (even new ones) been load tested with a proper high voltage test apparatus ?(Merc-o... or mohat box)
so when did all this start happening ? after some maintenance you did or suddenly ?
try an extra grd wire ( flexible mesh) between mag plate and engine frame.
have you swapped one circuit with the other to see if it is a position related issue or component related ?

 

[Crosbyman]

see chat gpt reply...

​

what would cause a 1973 40hp Norseman ignition to fail intermittently on one cyclinder

​

On your 1973 40hp Norseman (Evinrude/Johnson-era motor under a different badge), intermittent ignition failure on one cylinder usually comes from the ignition system rather than fuel, since the other cylinder runs fine. Here are the most common causes, in order of likelihood:

Possible Causes​

1. Cracked or failing ignition coil
   • Old coils on these motors often develop hairline cracks. When they warm up, insulation breaks down and spark fails intermittently.
   • Check the suspect coil for cracks or carbon tracking.
2. Points & condensers(if still original, since many of these motors were still breaker-point ignition in 1973)
   • Dirty or pitted breaker points → weak/inconsistent spark.
   • Worn rubbing block → incorrect gap.
   • Weak/bad condenser → spark will drop out under load, but may return when cooled.
3. Loose or corroded wiring
   • Check the primary wires from points to coil. A frayed or loose connection can intermittently cut spark.
   • Look for pinched wires under the flywheel.
4. Weak magnet or dirty flywheel key area
   • Rare, but a flywheel that has shifted slightly on the crank (partially sheared key) can change timing on one cylinder.
5. Spark plug / plug wire issue
   • Bad plug, cracked porcelain, or old carbon-core wires.
   • Swap plugs/wires between cylinders — if the problem follows the part, you found the culprit.

---

How to Diagnose Step by Step​

1. Spark test → Use a proper adjustable spark tester (should jump 7/16” gap with blue spark). Check when hot and cold.
2. Swap components → Swap coils, wires, or plugs between cylinders to see if the problem moves.
3. Inspect under flywheel → Clean and check points (set to 0.020”), and check condensers.
4. Heat test → Many ignition parts fail only when hot. If spark disappears when the motor warms up, suspect coil or condenser.

---

9 times out of 10 on a 1970s OMC-built motor, an ignition coil or condenser is the culprit for intermittent single-cylinder failure.

 

[racerone]

??----NORSEMAN is just the Evinrude name given to the 40 HP models in the early 70's.----Like all Evinrude models, used a motor name.---Starflite , Triumph, Fisherman , Skitwin , Big twin , ETC , Etc.

 

[Crosbyman]

1973 40hp Norseman (Evinrude/Johnson-era motor under a different badge),

 

[geoffwga1]

see chat gpt reply...

​

what would cause a 1973 40hp Norseman ignition to fail intermittently on one cyclinder

​

On your 1973 40hp Norseman (Evinrude/Johnson-era motor under a different badge), intermittent ignition failure on one cylinder usually comes from the ignition system rather than fuel, since the other cylinder runs fine. Here are the most common causes, in order of likelihood:

Possible Causes​

1. Cracked or failing ignition coil
   • Old coils on these motors often develop hairline cracks. When they warm up, insulation breaks down and spark fails intermittently.
   • Check the suspect coil for cracks or carbon tracking.
2. Points & condensers(if still original, since many of these motors were still breaker-point ignition in 1973)
   • Dirty or pitted breaker points → weak/inconsistent spark.
   • Worn rubbing block → incorrect gap.
   • Weak/bad condenser → spark will drop out under load, but may return when cooled.
3. Loose or corroded wiring
   • Check the primary wires from points to coil. A frayed or loose connection can intermittently cut spark.
   • Look for pinched wires under the flywheel.
4. Weak magnet or dirty flywheel key area
   • Rare, but a flywheel that has shifted slightly on the crank (partially sheared key) can change timing on one cylinder.
5. Spark plug / plug wire issue
   • Bad plug, cracked porcelain, or old carbon-core wires.
   • Swap plugs/wires between cylinders — if the problem follows the part, you found the culprit.

---

How to Diagnose Step by Step​

1. Spark test → Use a proper adjustable spark tester (should jump 7/16” gap with blue spark). Check when hot and cold.
2. Swap components → Swap coils, wires, or plugs between cylinders to see if the problem moves.
3. Inspect under flywheel → Clean and check points (set to 0.020”), and check condensers.
4. Heat test → Many ignition parts fail only when hot. If spark disappears when the motor warms up, suspect coil or condenser.

---

9 times out of 10 on a 1970s OMC-built motor, an ignition coil or condenser is the culprit for intermittent single-cylinder failure.

Been through all of the above,New coils,new condensers,points completely removed,dressed and polished all wires to coils checked and tested,plug boot tested,even swapped flywheel.Still no spark.I am going to try with several different condensers though I have fitted new ones as I know they can be troublesome.I will keep you posted on progress.