2 cylinders runs rough and sputters, 1 cylinder runs fine

[Biksco]

I've got a Johnson 60 hp 1982 2-cylinder J60ELCNM outboard.

The engine runs rough and sputters with both spark plugs connected. If I disconnect the top spark plug, the engine runs smooth on the bottom cylinder only.

Is this an electrical or mechanical problem? What should I be trying?

 

[oldboat1]

Check for spark on the top cylinder, and measure spark to test the ignition strength. Use an open air adjustable tester available at auto parts stores. (Same test for the bottom cylinder, while you are at it.) When testing, remove both plugs.

 

[jimmbo]

You're saying it runs smoother on only one cylinder, than it does when both are supposedly firing?

 

[oldboat1]

Auto parts stores will loan or rent out compression testers. Get compression numbers for both cylinders, and post them -- like measuring spark, test with both plugs removed. Crank just until the needle on the gauge stops, and record the number.

 

[racerone]

Check fuel pump diaphragm.

 

[Biksco]

Compression: Bottom cylinder was 125, top was 115. (top was having the running issue) Brand new spark plugs, gaps checked.

You're saying it runs smoother on only one cylinder, than it does when both are supposedly firing?

Right - the bottom cylinder runs fine by itself, it seems the top cylinder Is "misfiring" or causing something to make it "sputter occasionally" when it runs with the bottom or itself.

 

[hardwater fisherman]

If the fuel pump is run off the top cylinder it may be leaking fuel into the cylinder as suggested in post #5.

 

[Bosunsmate]

check timing, if the powerpack goes bad it can be irregular/out of time on a cylinder

 

[racerone]

Compression should be 140+ on those motors !!-----Time to have a look in the cylinders.

 

[Biksco]

Hey Guys! Thanks for all the suggestions! I'm doing this for my non-computer savy neighbor. I shot this video showing and explaining what's going on:

 

[Bosunsmate]

Good video
But dont rev the motor like that in neutral, it can do whats called a runaway and get overspeed and self destruct. Turning the key off wont stop it then as its so hot itl be self igniting. The only way to cut it off then is to pull the fuel line or shove a towel in the carb throats.
What happens when you disconnect the lower plugcap but keep the top one connected?
Also when you disconnect them always ground the cap onto a bolt or something. Not doing so can damage the electrics.
Looking at what happens in that video id say my earlier thought of the top cylinder being out of time seems most likely cause of the issue
Ive this same motor as this gentleman. I find it very robust

 

[Biksco]

What happens when you disconnect the lower plugcap but keep the top one connected?

He did that at the very end - the engine died.

Looking at what happens in that video id say my earlier thought of the top cylinder being out of time seems most likely cause of the issue

OK, how does one fix "out of time"?

Thanks for taking a look!

 

[oldboat1]

It appears the motor is being tested by opening the carbs alone, not rotating the timing plate. Along with risking a runaway (above), would not be able to test operation that way -- certainly not timing.

 

[Bosunsmate]

Ah so he did pull that off. Ok compression doesnt seem the problem.
To test timing you need a timing light, they are not that expensive to buy or hire.
If it is something wrong with timing on just that top cylinder itd be either the trigger sensor or the powerpack. Its normally the powerpack, which is that black rectangle shaped unit you can see near the end of the video.