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1968 Johnson 3hp Spark Gap Jump Test

S

Swarlos

Regular Contributor
I'm suspicious that my 1968 3hp Johnson outboard is only firing on one cylinder. It's hard to start and it doesn't have much power. I realize 3hp doesn't give much power, but I have a 14' aluminum v-hull that barely crawls on full throttle.

I went through a full carb rebuild and new head gasket (improved compression from 60 to 70 on both cylinders), when I did a spark test, both cylinders would get a bright blue spark at 1/4" gap, but the bottom cylinder got nothing at a 3/8" gap.

Is 1/4" gap good enough for this model or should I pull the flywheel and check the magneto? I don't really know what I'm looking at in there, but I don't want to replace the coils, points, and condensers if I don't have to.

Thanks in advance for the help!

P.S.
I realize after writing this that I could test it firing on only one cylinder by removing the lead to the spark plug on one cylinder at a time, but the lake is frozen solid right now and I don't have a great setup to test in a bucket. It may be better to let this wait until spring.
 
Well you can pull the flywheel off, and check that breaker points are good condition and that the cap is right. If points are bad, then it is time to replace them and also condensators, all of these are not expensive and easy to find. Now when the flywheel is off, check also that your coils looks good, i mean no cracks, and look carefully that coil wires are good condition, also check your spark-plug wires. These 3hp engines really runs so smooth, that it is not easy to tell if it runs with all cylinders or not. I have 3hp from 1966, i know it runs with all cylinders, since both spark plugs looks similar. I did re-build to my engine, you can see my project from here:
http://www.marineengine.com/boat-forum/showthread.php?451657-Evinrude-3hp-1966-rebuild
I hope that you will get your engine work well, these are super good motors. Merry Christmas to everyone
 
Hi to my friend there in Finland, very good mechanic on these motors for sure. Often times the coils will crack and/or a pin hole will form allowing high voltage to escape to the stator plate underneath the coil. This may only occur when motor is idling or mid speed and not show up on the pull cord test because you are not spinning it fast enough to create enough high voltage to jump through the coil shell. On occasion, the coil may arc internally.....once again, when it is running and not with a "slower spin" when pulling the rope start. This is a more common problem with certain replacement coils with cheap coating on internal windings.
 
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If you get a consistent spark on a 5/16" gap like a small electrical storm. ----And a snap, snap you can hear , you are good to go.
 
I tried 1/4" and 3/8", but I guess I'll try 5/16" to see how it goes. Should you be able to hear the snap over the sound of pulling the rope?

I think I will pull the flywheel off and have a look around. Hopefully any potential problems will be apparent. Would I see any scorching associated with the high voltage taking a broken path out of the coils?
 
Does it jump the 1/4" gap consistently ?-----Coils should be removed to check the bottom for what I call ---" burn through " --to ground
 
I did 3 good sparks on 3 pulls at 1/4". I increased the gap after that because I thought it was supposed to be 3/8" for a good test.
 
I pulled the flywheel today and had a look at what was underneath. It looks like coils, condensers, and points were all replaced a few years ago. I saw a few things that looked strange to me.

Bird's eye view: https://ibb.co/BzB2YK5

Crusty looking cable: https://ibb.co/18CWn8W

Bent metal on coil: https://ibb.co/FBdC4wX

Piece of insulation?: https://ibb.co/crFSspC

It looks like I need to replace one coil, can anyone tell me what that yellow fuzzy stuff is? It looks like insulation or something.

I think I should check breaker points adjustment while I'm in here, but I don't know how. Does anyone have pointers, or a link to a tutorial?


Thanks
 
I think your " insulation " is in fact a wick to lubricate the cam for opening the points.----The condensers look ancient to me.----There are numerous tutorials on this wonderfully simple magneto.----Don't loose the bracket that holds the wick.-----They are very proud ( $$$$ ) of them.
 
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You say the condensers look ancient, what makes you say that? My assumption that work had been done recently is that everything seems very clean and unworn, but maybe electrical components in a closed environment will look clean and unworn for decades.
 
Those tall ( red top ) condensers have not been available from the factory for over 40 years.-----That is why I say they appear to be " ancient " here !!
 
I guess I'll replace everything for peace of mind then. Coils, points, condensers. Anything else I should replace while I'm in there?
 
How do the spark plug wires look? Sometimes they are not spun all the way into the coils, or can arc to ground somewhere, or oxidize/corrode at the spark plug boots. Those old condensers were darn good, I have a box full of them I replaced for fun. Probably not your problem. That particular coil replacement is also better than everything out there that I have ever used. My guess is points or wires. Make sure that little wire going from the coils to the points is not rubbing or pinched. Points clean with no pitting and set .020 at the index point on the ramp. I lube the points post with a tiny bit of synthetic grease....only because I want things to last a few days shy of forever. Any oil will do for cam follower wick, one drop. I use a synthetic Amsoil like my 2 stroke premix "Saber". Use that as well for your pre mix with non oxy petrol at 50:1 mix. If you burn up the motor I'll send you a new powerhead. I run 64:1 in my 3's, done it for over 40 years. Change spark plugs once every year.....needless to say I have a huge tray full of perfect "used" plugs. Stupid? Maybe.....but only before I started using Amsoil.
 
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timguy said:
How do the spark plug wires look? Sometimes they are not spun all the way into the coils, or can arc to ground somewhere, or oxidize/corrode at the spark plug boots. Those old condensers were darn good, I have a box full of them I replaced for fun. Probably not your problem. That particular coil replacement is also better than everything out there that I have ever used. My guess is points or wires. Make sure that little wire going from the coils to the points is not rubbing or pinched. Points clean with no pitting and set .020 at the index point on the ramp. Any oil will do for cam follower wick, one drop. I use a synthetic Amsoil like my 2 stroke premix "Saber". Use that as well for your pre mix with non oxy petrol at 50:1 mix. If you burn up the motor I'll send you a new powerhead. I run 64:1 in my 3's, done it for over 40 years. Stupid? Maybe.....but only before I started using Amsoil.
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You think that coil is fine with the weird blemishes on the cable and the top of the metal bent up like that? I'd be happy to leave anything that doesn't need to be replaced.
 
????----That little bit of metal bent up on one coil is insignificant.------Time to sit down and look at / study some " how to " videos on youtube.-----When you understand how this wonderful magnet works ( in production for 40 years ) it will all become easy for you.
 
Don't see any problem with that and the screws that hold down the coils looked like a dam careful mechanic did the work. My feelings, if I mark a screw it's a big "bad".
 
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A shop with a " MERCO-O-TRONIC " ---I have 2 of them, magneto analyzer can test the coils for you.-----But these coils are not expensive and it would be cheap to replace them.-----I suggest you study how these magnetos work.
 
Racer is highly respected here. He probably witnessed the first Mercury motor in 1939. New coils are a good call, but there are a lot of crappy replacements offered out there too so be wise. Points can be checked with an ohmeter for zero resistance. Condensers can be checked for charge and discharge.
 
Racer is highly respected here, been around awhile. He probably even saw the first Mercury motor roll out in 1939.
New coils are a good call, but there are a lot of crappy replacements offered out there too so be wise. Points can be checked with an ohmeter for zero resistance. Condensers can be checked for charge and discharge........and leaks..... I made a tester. Condensers/capacitors are pretty reliable, and a very important piece. Don't get me wrong, I'm pretty experienced but still learning from seniors here on the forum.
 
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Just a visual check of your pictures, my opinion that all those parts are original to that motor. Those purple coils were some of the best OMC ever made. Do you have and know how to use a multimeter to check the resistance? If resistance is ok, my bet the coils are ok. I'll bet the condensers are too. In fact, I'll bet the whole thing is. You might check the breaker point gaps. In short, there might not be anything wrong with the ignition. You need to run it and do a cylinder drop test to confirm it actually is (or not) running on one or both cylinders.
 
Agreed, Gator. I remember these coils. OMC came out strong after the brittle/shrinking material that coated the early coils. I think 67 or 68 may have been the years it was introduced. The screws are too "mint" to have been R&R'd by almost any mechanic I have ever known. That damage to the coil is unexplainable, unless the coil was dropped on a cement floor from 4 feet high. This looks like a very "virgin" little motor.
 
fdrgator said:
Just a visual check of your pictures, my opinion that all those parts are original to that motor. Those purple coils were some of the best OMC ever made. Do you have and know how to use a multimeter to check the resistance? If resistance is ok, my bet the coils are ok. I'll bet the condensers are too. In fact, I'll bet the whole thing is. You might check the breaker point gaps. In short, there might not be anything wrong with the ignition. You need to run it and do a cylinder drop test to confirm it actually is (or not) running on one or both cylinders.
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I think there's a multimeter around here somewhere, but I don't have any experience using it. I'll google some multimeter tutorials. We're having a heatwave right now, so I could actually set up a barrel tomorrow. Thanks everyone for the input.
 
We all love these old motors, the simplicity and enjoyment to repair as well as admirable engineering that makes us smile. Proof it's good.......still around after 50 years.
 
I am always happy to help people with these nice motors, so i want to show you some photos which i took during my engine rebuild. These photos are about my ignition system, and during project i made notice that the previous owner of my motor surely was renew the ignition system. All i need to do was put one new coil, ( the coil with white paper), since the ground wire of the old coil was almost broken. Okay, now the photos

1.jpg
This is taken at during disassembly, i am sure that the black/dirty oil under ignition stator plate was due to the leaking crankcase upper seal

2.jpg
Ignition system is ready to put back. Coil with white paper is new, original Evinrude part.

3.jpg
Everything is clean and nice, before putting stator plate back.

Now i really dont know how i can take off the "attached thumbnails" window.
 

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Thank you everyone for your advice. A year ago I knew just about nothing about outboard motors. I got sick of depending on the local shops to keep them running so I decided to work on them myself. I still have a long way to go before I know enough to do work without asking advice, but I'd never get there without your help.
 
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