Sort of rough running 120hp Johnson

[mischmerz]

Howdy -

I am restoring a '83 200XF with an 120hp Johnson original motor. It still has good compression and runs well. However - I recently noticed the sound changing slightly while dropping about 50 to 75 rpm. It goes from a clear sowing machine sound to something more rough sounding - for some time (variable, 20 to 40 seconds), than back to sowing machine and after a little while back to rough. Increasing throttle always switches to "sowing machine" for a moment, before going into rough again and dropping some rpms. So I suspect carburetors? A friend suggested spark plugs .. what do you think?

Thanks.

Michaela

[fitz73222]

Hi Michaela,
It could very well be a spark plug misfire. They're cheap enough to replace. If the engine is also an '83, I believe it uses Champion L77JC4 plugs but that is easy to verify. Pull the plugs and see if they are black and sooty. They should be variant of golden brown color. The easiest thing to do is to isolate a fueling problem from an ignition problem is to run the engine from another fuel source such as a remote 6 gallon tank with fresh fuel and a known good fuel line. If your engine is an '83 then it is not oil injected and you have to mix the oil and gas correct? Try running the engine on a different tank and see if the running quality improves. This will point you in a direction. They key is do one thing at a time and test. There are many things this can be but for now I'll avoid those details until after you do the plugs and fuel experiment.

[Levi]

Also and I am not downing this site but there are TONS of REALLY SMART guys on Iboats forum who can and will happily walk you through a step by step troubleshooting of your engine.

[mischmerz]

Hmm .. thanks Levi. I posted the question in iboats but the answers were less that "knowledgeable". More like asking a doctor what to do for a broken arm and he suggests two aspirin and lots of fluids. Won't do any harm, but won't help a lot either.

So - I'd rather stick around here. Much less traffic but more knowledge

Michaela

[fitz73222]

Hi Michaela,

Thanks for the plug for our site. Speaking for some of the others who help out with technical advice here, I can vouch that we help from personal experience and not conjecture so when we lend a hand, we know it to be true. So to bump this along, have you had a chance to try any of the initial troubleshooting ideas to get you started down the path to sewing machine running again?

Farley

[mischmerz]

Hey Farley - well I checked the spark plugs and they "look" like they're ok. Since most of the ignition parts are new (not the plugs though) I am going to change 'em anyway. From what I remember from repairing my motorcycle back in the eighties, when you push the gas lever forward, the carburetor squishes a bit of additional gas into the system. I assume this is true for my vintage Johnson as well? Since pushing the accelerator forward instantly leads to a few seconds of "sewing machine" mode,  I suspect dirty carburetors. My motor just has two, so cleaning them might not be a big issue. I am sure there's a Youtube video giving all the information I need.

Michaela

[fitz73222]

On outboard carburetors, pushing the throttle open only opens the butterflies to allow more air in. No additional fuel is delivered like an automotive accelerator pump that physically shoots gas into the venturi. Your engine uses 2 double barrel cards to feed the engine and they are very simple to recondition. I would try the remote tank test first before tearing into the carbs. Usually, carb issues manifest as poor low speed idle with a cough or sneeze intermittently, hesitation on throttle advance or the need to choke the engine to keep it running. If you're using ethanol fuel then the entire fuel system is suspect for degrade and contamination.

[mischmerz]

Oh - very interesting detail. Thank you. The tank, the fuel lines, fuel/water separator - all new. It starts up right away, the idle is reliable, it may cough once or twice if is hasn't run for a week or two, everything works reliably and good. It's just that little drop in rpm (say .. from 4300 to 4250 - barely noticeable) and the accompanying change in sound.

m.

[mischmerz]

Finally. Got it fixed. The stator was to blame. Seems a wire was broken and it made the ignition system cut out due to vibration. Put in a good used stator in and my max RPM is back to a solid 5300 RPM. Thanks for all the suggestions and help on- and off board.

Michaela

[smccall]

Boy.. how on God’s green earth does someone diagnose a broken wire on a stator? Pulling the flywheel and looking and seeing it visually? Everyone should have a remote tank coupled with a known Good fuel line not only for diagnostics but for emergency purposes to get you back to the ramp. Or at minimum a fuel line and primer bulb as they don’t take up much space. Just wondering how Michaela got a clear diagnosis without throwing good parts after good parts. Also, is a stator repairable? He mentioned just one broken wire.I’ve seen em for sale and they’re not cheap. I get the fact being safe is far better than being sorry. Michaela’s insight will probably be very valuable. I bring this up despite possibly looking like a novice. I hope Farley ways in on this as well. As he’s a great resource and certainly helped me in the past.