115 hp Johnson Missing

[goblerblaster]

My 2000 model 115 Johnson ( model number JL115PLSSB) has developed a miss, but not all the time. I have cleaned the gas tank out, run Seafoam, B12, and Evinrude conditioner thru it - on different tanks of gas- and it still is missing. The pattern is that it starts easy and idles fine. I can throttle it up hard and normally not have any missing. I can drive it at various speeds with maybe only an occasional miss for 15 or 20 minutes. THEN, just about the time I think it is running great and must be fixed- it will start to miss. Seems the longer I keep driving it the worse it gets. This pattern has been repeated about 5 or 6 times.

I also checked all the carb bolts to make sure they were tight, all fuel line hoses and clamps, etc and cannot find any air leak. I have ordered carb kits, but am beginning to think carbs may noy be the problem.

Any suggestions? Could this be a faulty power pack? If so how do you check to see?

 

[interalian]

Sounds like ignition. When modules are marginal and get warm, they can fail. I would hang a timing light on it when it's misbehaving and check for spark dropouts, one cylinder at a time. You may trace it to only one cylinder. If you can isolate to one cylinder, you can try swapping the dual coil and see if the problem moves with it. If it doesn't move, look to the pack or perhaps just a bad connection. I like to R&R connections that haven't been disturbed for a long time as it can break any corrosion that may be on the pins.

 

[mrcj001]

check the ignition coils for cracks or leakage.....when they get hot , they will start to fail

 

[goblerblaster]

Even when it starts to miss pretty bad at 4000 to 5000 rpm, it will still idle without missing at all. Still think that is ignition? I don.t want to put in carb kits if the bulk of responders think that is not the problem. Thx for any help

 

[weaverunner]

interalian is spot on - sounds like it's ignition related. Most likely culprit is going to be your power pack. When power packs or ignition modules begin to fail, it'll be more apparent as the motor/power pack heats up. With your symptoms showing up after running the motor for 15 minutes, it sure sounds like a bad power pack.

 

[goblerblaster]

UPDATE:
​Thx for the responses. I thought I would try a new coil and switch it from one coil position to the other- since that is a lot cheaper than a new power pack. I ordered one , waited a week for it to get here, put it on the motor and found the new coil was BAD !! So, now I am at the waiting on another coil to arrive. Since I am anticipating that it will ultimately require a new power pack I have been looking and pricing them. I have seen where some power packs include the "optical Sensor". What does that part do and is it something that normally fails? Also, I noticed on some ads that there was a warning of " do not run motor without plastic cover being installed over sensor and power pack".. Why does this make a difference? Also, I checked the continuity of the plug wires with a volt meter that has the scale and needle. The needle pegs out when I touch the meter leads to each other, but only goes about half scale on the plug wires when putting one lead on one end of the wire and the other lead on the other end. All wires were the same however. Is this normal?

 

[flyingscott]

Yes you want to replace the optical sensor. The optical sensor controls the timing and they do tend to fail.

 

[goblerblaster]

so, what is the problem with running the motor with the plastic cover off that covers the coils and power pack??