1972 Johnson 4HP - No Spark

[JTKelleyiii]

I recently purchased a 1972 Johnson 4HP for a very good price. Seller told me it would not start.

Compression on both cylinders is appx 92 psig. Solid.

The problem I am having is that when I pull the starter I get no spark on either cylinder. I hooked up an adjustable gap tester and see nothing regardless of gap width.

I pulled the flywheel and looked over the magneto assy. Everything looks clean and intact. Points look good also.

Before I start a wholesale replacement of ignition components I have a question. When the speed control lever on the port side of the engine is in the stop position, what is that physically doing? Does that short the coil primaries to ground? If so how is that happening? I am wondering if this is somehow killing my spark even when the lever is in the run position.

This ignition system appears to be fairly simple and want to make sure I am not missing something simple.

Any info or thoughts on this would be most appreciated.

Thanks

 

[Rick.]

Re: 1972 Johnson 4HP - No Spark

Your throttle lever is on the Starboard side. Actually that's the only thing I'm sure of. I've a 71 Evinrude and I have not seen anything on it that would ground the coils to stop. When it's moved to the off position it starves the motor of air and fuel thus stopping the engine. It is really unusual to loose spark on both cylinders at the same time. I trust you checked both? On the port side just behind the recoil there is a clamp that holds the plug wires to the bottom of the magneto plate. There is also on the same screw a stainless steel strap that should go to the top side of the brass armature plate. I just discovered this last week and mine (ground strap) was not contacting the armature plate. Once I got it to rub on the brass armature plate my spark improved in strength. I am certain I am the one that put it back in the wrong position in the first place. Best of luck. Rick.

 

[JTKelleyiii]

Re: 1972 Johnson 4HP - No Spark

Rick,

Thanks for the feedback. You are correct, lever is on Starboard side.

Both cylinders were checked and have no spark, regardless of adjustable spark checker gap width. Thats what made me wonder about something that might kill the spark other than components (something like a kill switch).

To start with I am going to clean points and ensure the gaps are set correctly and definitely check the grounding strap and go from there. Like I said, this is a really clean little motor with good compression. The plugs that came with it must have been changed during the no start troubleshooting by the PO since they look like they have never been fired. I suspect this will be a simple fix once I find it. Will post results.

Thanks Again!

 

[lindy46]

Re: 1972 Johnson 4HP - No Spark

No "kill switch" on that motor. Something is wrong under the flywheel.

 

[JTKelleyiii]

Re: 1972 Johnson 4HP - No Spark

No "kill switch" on that motor. Something is wrong under the flywheel.

I agree.

Looked for that grounding strap that Rick mentioned and it is not installed. I suspect the ignition system had been worked on at some point, based on how new the components look, and during reassembly the grounding strap ended up as a bonus part.

I would think that not having this part installed could have an impact on the no spark situation. Will get one and install and see what happens.

It is surprising that the the manual neither shows nor mentions this part. The only place it shows up is on parts list and in the minds of men experienced with this type of ignition.

What a great website. I am completing getting my 135HP Johnson running right and am now moving onto the 4HP. After this I have a 1975 135HP Evinrude Silver Starflite to work on. While I have service manuals, without the information I have gleaned off of this website these jobs would be a whole different ballgame.

Thanks to all

 

[Rick.]

Re: 1972 Johnson 4HP - No Spark

Be careful when you order the strap. You may have noticed (on the BRP parts site) the thing is named wrong. I'm not sure if the numbers are wrong too but you should bring it to the dealers attention so you don't end up with a plug wire holder. On my 4 hp I still had spark but weak and very weak on the top plug. I do hope that will help you but you could probably just put a jumper wire from the armature plate to the screw to see before you go and order the strap. Rick.

 

[JTKelleyiii]

Re: 1972 Johnson 4HP - No Spark

Once I looked harder I did see that the grounding strap is present. Removed the flywheel again and noted grease all over armature plate and elsewhere. Cleaned everything off and put new points, condensers, plug wires and boots. Tried out and had strong blue spark on both cylinders! Not sure what the exact root cause was but like many recommend, putting in a tune up kit is the right thing to do on an older unknown magneto ignition.

Unfortunately, even with strong spark it would not fire. Plugs were completely dry. Disconnected fuel hose at carb and pumped bulb. Plenty of fuel. Tore down carb and float bowl was dry as a bone indicating to me a stuck shut float valve. Rebuilt carb, which was quite clean, and installed. Motor started on third crank! Nice and smooth and quiet.

Gonna change out gear case oil, water pump impeller, and recheck point settings then it should be good to go. Gonna use it as a kicker on my 15 1/2 ft Manatee and to allow me to move around on the shallow edges of the marsh for fishing.

These little motors are fun and relatively painless to work on compared to the old 135hp v4. Really enjoying bringing this little bugger back to life.

Thanks

 

[Rick.]

Re: 1972 Johnson 4HP - No Spark

Great to here you're up and running. Would be nice to know what exactly the problem was but that isn't always clear. They are great little motors and very fuel efficient for trolling motors. Rick.