1988 Johnson 140 miss at idle; spark plug dry black sooty

[mbecke2]

FINALLY got some life back!! Man, crossing the orange coil wires makes a HUGE difference. So now she starts perfect and runs ok but I can still here a miss at idle. When it misses it makes a loud pop and shoots out extra exhaust from the propeller and shakes the motor. Does this pretty regularly about every 2 seconds. I evaluated the spark plugs and cylinder 3 has black powdery soot all over and the other 3 plugs look ok. I took the motor to a mechanic and he noticed a miss on cylinder 3 and said it was the power pack. Well I changed the ppack and no difference. I also changed the stator. Every cylinder seems to have spark using a spark gap tester set at half inch. BUt maybe once it starts, it has a miss on cyl 3. What could cause this? I changed everything in ignition system (coil, plug, wire, ppack, and stator) except for the timer base/trigger. Is this cylinder running rich?? Is this an electrical issue. How do I check the spark on all the wires while it is running?? Thanks for replies.

 

[Joe Reeves]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

With engine running, use insulated pliers (plastic or nylon) to remove the spark plug boot from the spark plugs, one at a time, then replace them. You'll be able to hear a drop in power (should all be even) and you'll hear/see the spark.

That engine requires having the carburetor face plate installed in order to run properly and the thick rubber gasket must be present between that face plate and the carburetors, otherwise the carbs will run lean.

The exception being to test a lean running carb..... have the face plate removed, then srtick two fingers into the carb throats, one carb at a time (acting as a manual choke). If on any carb, the rpms pick up some and the engine smooths out somewhat, that particular carb is running lean.

 

[bmstang]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

Try changing out all the spark plugs with new. I had a similar problem changed the plugs and it solved the popping.

 

[boobie]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

You can use an inductive timing lite and when mtr is running use your ears and the lite. Hook to each cyl and watch the lite. When you get to the cyl that is missing you'll also see it in the lite indicating an ignition missfire.

 

[Dhadley]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

Black soot indicates an air leak. Could be coming from the side cover on the carb, not uncommon. Remember the front half is an X half, #3 carb is on the port side.

 

[mbecke2]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

Im not sure if it SOOT, it is more like dry black powder but the other 3 are black wet oily. I am sure that is has a miss at idle and a certified OMC dealer mechanic told me it had a miss on cyl #3 and he wanted to change the ppack, but I didnt wanna spend 1000$ so I changed it myself. Well Im pretty sure it still has the miss and its probably cylinder 3 because the spark plug looks way different than the other 3. What could cause just cyl# 3 to miss. Im pretty sure I moved the carbs around to see if it followed and it did not. Stayed at 3. Leads me to believe ignition problem, but I have changed everything except timer base. Oh and the mechanic changed the spark plugs so I guess that wasnt it. Also I think I noticed the #3 carb leaking fuel when I primed the ball indicating float was not adjusted right. Maybe this is the problem?? I just want to be sure the ignition is firing and then move to carbs. I guess I can try to cover each carb while running and see if the motor picks up rpm as suggested by Reeves. I'll have to go take a look. Running out of time. Duck season starts in 20hr 11 minutes and counting!!!!!!!!!

 

[surrender]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

Pull the plug wires will running one at a time to see if your getting fire to that cylinder. Also, while running wiggle the wires coming from the PP to your coils. the connector at the coil(almost a mini spark plug like connector) can become loose(it did on mine and caused your exact symptom). I pulled the mini boot and cleaned it up and crimped it down a little so it fits tighter on the coil. All four fire nice now and no miss. If you need those connectors, suprisingly, you can find them at Radio Shack. They dont carry the boots so dont tear them getting to the connector.

 

[Dhadley]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

Yes, you are describing soot which comes from an air leak. But we have a question - are you trying to force the motor to idle down (rpm-wise) while running it out of the water on a flushette?

And obviously the float issue needs to be addressed. FYI - don't run the motor under a load with the airbox cover off.

 

[mbecke2]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

Dhad- Actually I ran the motor with rabbit ears and could easily hear the miss and see the extra spout of exhaust shoot through along with the miss. So I then ran it in a tank of water and could still hear the miss, but I'm not sure if this miss is "normal" or if there is a problem. I put the airbox back on and everything back together but I havent had a chance to run it again. I'm going tomorrow in a friend's boat. Not sure what you mean by "force it to idle down" but I screwed the idle screw all the way clockwise till it cant go anymore so thats as low as it will idle. It starts perfect and runs all day long, but I dont like that miss. I wanna say its something in the ignition thats causing the spark to miss on that plug, but Im having trouble isolating it. Or could it be that cylinder needs to be reworked (new valve and rings)? Anycase, the sparkplug is black dry powdery looking. When I get more time to fiddle around Ill update whats goin on and maybe upload pics. My friend says he thinks my problem is fixed and the motor is ready to run on the water, but I lack confidence since it hasnt run right since April. That cylinder 3 has me baffled. Only thing I have not changed is timer base.

 

[Dhadley]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

OK, don't worry about the idle speed on a flushete or in a tank of water. That motor will idle fairly high with no backpressure in the exhaust. Once in the water the rpm at idle will come down naturally. Out of the water it'll idle at about 1200 or so once it comes out of Quick Start. If you are trying to force it to idle down out of the water it'll do wierd things.

Take care of the float issue first.

 

[mbecke2]

Re: 1988 Johnson 140 miss at idle; spark plug dry black sooty

I ran it again today on the rabbit ears and it didnt sound good. It started reving up and down by itself and I wasnt touching anything. In fact the throttle lever was all the way down and the idle screw was turned all the way clockwise. Finally it ran away and reved up really high and i pulled the key and it kept running. So I had to turn the red lever on the choke solenoid to get it to kill. Still starts and will run on rabbit ears, but sounds really bad to me. Again I checked the plugs and again cyl 3 plug is dry black powder completely covered. I will try and run the motor on the water sunday and i will update. Thanks.