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1986 Johnson 120 problem

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RobertO5031

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I have a 1986 Johnson 120 outboard and I'm having a couple issues with it. When I start the engine it has an extremely rough idle for the first 5-10 minutes. The engine will go from a high idle and then almost stall and then save itself about every other second. It does it both on the hose and out in the water. After it finally comes down the engine runs well but doesn't quite hit top speed. It only hits around 5500 rpm.

I suspected the problem for speed could have been with the linkage. So I adjusted the screw where the throttle cable enters the engine bay. It ran better but then I couldn't get the idle down. The idle adjustment screw up by the flywheel was already set as low as it could be. I didn't like it idling at 2000 rpms so I set it back to where it was.

The compression is good, I replaced the spark plugs and gapped them to OEM Specs, and cleaned the carbs. Does anyone know what the problem could be? Thanks

-Bob
 
Found the part on ebay really cheap. It was OMC part # 394385 the fuel manifold. I should get it next week and have it installed for next weekend.
 
Hi Bob, I watched your video on You Tube and your engine exhibits the exact same problem as mine. I have a 1986 Johnson 140, I believe our engines are identical in every way except yours has a few components that reduce the hp to 120. My post is at http://www.marineengine.com/boat-fo...986-Johnson-140-Coughs-and-Splutters-and-Dies
From the advise I have received from Bill (member ID: ko4nrbs) who forwarded an extract from a trouble shooting guide, it would seem there are two issues that can cause the problem:
1) the VRO sensor and temperature sensors have become faulty, or the Tan wires going to the Power Pack from the sensors is routed too near the spark plug HT leads or has gone to ground. The advise is to disconnect both brown wires from the PowerPack and start the engine. If it runs normally then you know it is one of the two sensors or their wiring. Simply replace one and see if the issues is still there. Once you find the issue disconnect the wires from the sensor and see if the issue is still there, if yes cable is grounding or routed near the spark plug, if no then the sensor needs replaced.
2) If that does not do the trick then you need a DVA Direct Voltage Adapter, which is used to measure peak AC voltage. Within my posting (hence giving the link earlier) Bill has listed all the web pages needed, starting with how to built the circuit so you can then test if the peak voltage from the Stator assembly is constant or drops when your engine starts to cough and splutter.

I am no expert so the advise I am passing on is what has been shared with me. I plan to test 1) above today to see if it is a sensor issue. I will post my findings.

Mark.
 
Thanks for all the help! I just got my fuel manifold in the mail last night. Hopefully I'll be able to install tonight and see if it still has the same problem if not I'll try what Mark is doing also. (I don't have a timing light) Again thank you for your help and let me know how it goes

-Bob
 
Bob hi, racerone is correct the only way I could tell that it was not a doggy coil or dodgy fuel feed was by using a timing light. When I connected the timing light I was very surprised, as the engine was dying no spark, when it kicked a spark, but this was the same when testing all four cylinders. Watching your video and how your engine behaves is a mirror to mine http://youtu.be/vwSKT48ihNM This link is of one of the better days, as after 5 seconds the engine starts to run normally. The coughing and spluttering with mine can be 5 seconds like here or minutes, then it clears itself. Do not worry about the smoke, the VRO was removed and my son filled the tank 70L (15.4 gallons) but he cannot remember if the mixture was 40:1 or 50:1 (he has a trials bike that is 40:1). Once the tank is empty I will spray SeaFoam through it to clear that all out and put a bit in the fuel tank too then refill using 50:1.
 
Bob hi - I have been going through the web and located this article http://www.thehulltruth.com/boating...rd-intermittent-no-spark-all-cylinders.html#b
This post by mkantar has done everything I have done and testing the spark using a timing light determined the intermittent fault was with the power pack. As they are relatively cheap I am going to replace mine as the similarities are so alike the chances of my issue being different have reduced significantly (I could still have the issue but the chances are much reduced as I have someone who has walked the road before). The 1986 Johnson 120 is almost identical to the 140, the only physical difference I believe is the carb setup. As yours is a 120 this is a match. I will replace the power-pack and let you know if I have had success.
 
Bob hi - did you manage to get your engine fixed? I ordered the PowerPack an after market unit made by CDI Electronics Part number 113-3101 and fitted it today. Although my engine is the 140 I am sure it uses exactly the same Power pack (you would need to check). Fitted it to my engine and running off the garden hose was as sweet as you can get. I am going to do a load test on the water later this week, this will tell if the issue is truly resolved. So far so good, all signs are I am getting to the source of the issue, in my case a faulty power pack.
 
Tested on the water this evening, ran the boat for 1.5 hours at 4000 rpm, then after the 1.5hrs of cruising thrashed the engine about a bit. Not a hick up, ran as sweet as I can ever remember her running. From standstill to full throttle and everything in between, so far all tests seem to indicate issue gone, the power pack seems to have been the route cause of my Johnson 140 kicking and stalling and the engine catching just as it is about to die. I believe your engine has exactly the same issue. If you get the timing light and find all cylinders make the light flash erratically in time with the engine kicking and stalling, replace the power back and I believe you 120 will be fixed.
 
Hi Bob, did you ever get your engine running correctly?

Just a short update, since replacing the power pack with the EDI unit (18-5892) I have had the boat in the water 3 times total of just over 7hrs, and flushed it on the driveway 3 times (boat is used in Salt water) and it is running very well. If you have not fixed your engine then do the timing light test and if all cylinders make the gun flash erratically but in synchronization to the engine catching and stalling then my advise is to change the power pack.

With the new power pack the rev limited is at 6700 (OEM unit is set to 6100), I noticed on the water WOT my engine will go to 6400 so I have decided to change my Prop not relevant to this thread so I will stop here). Please advise how you get on as I am truly interested in your route cause as my engine was so similar to what you were experiencing (just looking to learn).
 
Mark,

Thanks for all the help I bought the power pack and installed it. I haven't had a chance to get it in the water yet, but I ran it in the driveway and couldn't believe what a difference the powerpack made. The engine idled perfectly! Hopefully I'll be able to get the boat in the water this week and I'll let you know how it runs. Thanks for the note about the rev limiter I'll keep my eye on it and let you know what results I find.
 
Bob hi,

Thank you for the update, great to hear your engine is purring and not kicking about on the driveway. I am 99% positive you will be flying once you hit the water. I have completed over 12hours now with my new Power Pack and other than reminding myself that my engine is a gas guzzler, all has been great. On the rev limiter being at 6700, discovering my engine would pull to 6400 allowed me to up my prop knowing I would not overload the engine. I fitted a 4 blade Solas Titan SS HR 13x19 to give me more out of the hole acceleration without impacting my top speed. With the new prop my engine is naturally limited to 6100 (due to prop 4 blade drag) top speed is 3mph faster at about 55mph, engine cruises at 25mph at 3000 rpm. All speeds are off the speedo and not GPS (in reality I think I am doing about 52mph GPS, I will test though). Just sharing my experience todate :)
 
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