18 hp Johnson no spark

[twocyclemania]

I recently inherited a 1960 Johnson 18 hp outboard. I've worked on dozens of motors (though I'm not a certified outboard mechanic) and never had the following problem. The motor has no spark. I've replaced the coils, points clean and adjusted. I lightly sanded the top of the shaft and the inside of the flywheel mating surface to make sure it had good contact. No spark on either cylinder. I'm sure I'm missing something but I need someone to point it out. thanks

 

[racerone]

Wires going to the correct set of points ?----Cam upside down ?----Sparkplug wires replaced ?

 

[Crosbyman]

a 1960 18hp magneto probably has 2 condensers bad. ... unless of course they were replaced since the 60s...even done so in the 90's 34 yearsago.... they could still be bad.

proper testing of condensers requires high DC voltages to check from internal leakgae and such voltages are not found in common VOM meters. Best to just put in new ones.

If not replaced they should be. The johnson service manual available on line covers these magnetos extensively and is a good reference for anything to do for your oldy

1922-1964 Johnson 302231 Outboard Service Manual

Johnson Outboard Motor Service and Repair Manual # 302231 Tenth Edition covers all Models 1922-1964 .pdf download

watercraftmanuals.com

here ar a few bugs to check out

 

[Crosbyman]

take a ohms reading from plug boot clip to engine frame resistance should be 4-8 kohms depending of coils manufacturer

 

[Nordin]

As said above from racerone and Crosbyman and check if the low tension wires to the points and condensers has good insulation and not squeezed to ground.
When you changed the coils did you adjust them so the iron core rim is flush to the mounting lugs.
The gap between the iron core and the magnets in the flywheel need to be as tight as possible to build up a stronge magnetic field when rotating.

 

[kbait]

Bad kill button? Unplug connectors and test spark again..

 

[Crosbyman]

https://wrcoutboards.org/wp-content/uploads/2020/04/Part2_Condenser_Testers_And_Testing_Correctly.pdf

 

[ct1762@gmail.com]

a 1960 18hp magneto probably has 2 condensers bad. ... unless of course they were replaced since the 60s...even done so in the 90's 34 yearsago.... they could still be bad.

proper testing of condensers requires high DC voltages to check from internal leakgae and such voltages are not found in common VOM meters. Best to just put in new ones.

If not replaced they should be. The johnson service manual available on line covers these magnetos extensively and is a good reference for anything to do for your oldy

1922-1964 Johnson 302231 Outboard Service Manual

Johnson Outboard Motor Service and Repair Manual # 302231 Tenth Edition covers all Models 1922-1964 .pdf download

watercraftmanuals.com

here ar a few bugs to check out

but unless they are completely open/shorted, they should still allow it to spark? the ATOM ignition modules or the cheap Chinese copies pared with aftermarket coils solves this issue, starts much better, idles like a sewing machine, and never needs adjusting.

 

[Chris1956]

Condensers absorb the voltage when the points open, lessening the chance of arcing. This voltage is immediately dumped back into the ign coil, helping to induce spark. If the condensers are bad, you will have no spark.

They can be tested on modern digital multimeters, and roughly, on analog multimeters, however, they are pretty cheap, so just replace them.

 

[Crosbyman]

exactly... as the condenser insulation between the 2 foils degrades the strong EMF kick from the coil can't be saved nor contribute to the generation of spark energy when it dumps back into the coil.

Leakage can only be tested under high DC volage has explained in M.Moat's excellent articles in the Outboarder or the Westen region AOMCI see links .
Building is basic test box allows one to test and solve any suspect condenser problem. A simple idiot lamps will give a simple " go no go result".

https://wrcoutboards.org/wp-content/uploads/2020/04/Part1_Condenser_Construction_Failure_Modes.pdf

https://wrcoutboards.org/wp-content...2_Condenser_Testers_And_Testing_Correctly.pdf

https://wrcoutboards.org/wp-content/uploads/2020/04/Part3_Sizing_Condensers_Correctly.pdf

https://wrcoutboards.org/wp-content/uploads/2020/04/Part4_Repairing_Broken_Condensers.pdf

 

[racerone]

A MERC-O-TRONIC magneto analyzer does the testing.----Do not forget to heat soak condensers for testing !

 

[Crosbyman]

IF you have no accessto a Merc O Tronic tester here is a good video on building a inexpensive condenser test box... basically a AC voltage doubler/rectifier to generate a high DC voltage with a neon bulb similar to Mr.Mohat test box .

 

[Chris1956]

Gee, my newish digital multimeter has a capacitor test setting it reads in micro farads. A condenser used on magneto systems should be about .25 micro farads.

My old (1950s/60s) multimeter could be roughly used to test a condenser. You set it to resistance and touch the leads to the condenser wire and case to charge it. Now set the meter to DC voltage and switch the leads. You should see a momentary voltage reading if the condenser is good.

Just replace them.

 

[Crosbyman]

unfortunately the only significant test to do with a VOM is for shorts dead shorts ... anything else is mostly meaningless in the real world of operation under a flywheel !

I also have a capacitance reading VOM... but I only use it o determine the uf value but not the operating worthiness .

my Mohat box does the rest

 

[twocyclemania]

Thanks everybody for your replies. I did install new condensers. I've worked on many motors and can't recall a case where the condensers were bad (lucky?) but I replaced them anyway. Still no spark. I remembered other motors where the ignition wires had deteriorated at the spark plug boot connector. I pulled the boots and the wires didn't look great. I cut a quarter inch of of each and the copper wires looked new. I now have spark on both plugs. I should have eliminated that from the get go. I should replace the plug wires but for the meantime I'm just going to get her up and running. Thanks everybody for your help; appreciate it.

 

[racerone]

I have tested many condensers !---Found bad ones.----And I have often heard people say----" my motor is hard to start "----Or----" it is a 2 stroke and they are cold blooded and hard to start "-----Most motors when it good tune start right up if you have strong spark.