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  1. #1

    Default 1980 Johnson 85hp stuck throttle

    Hello everyone. My family has a 16" aluminum boat with a 1980 Johnson 85hp outboard motor (J85TLCSA) that up until recently was expertly maintained. Then due to my father passing away, it has seen little use the past few years. But last year I had a Marina do a complete clean/de-winterize of it, and we got it started with only a little trouble. It idled well and run full open throttle just great. So we took it back to the marina for winterization, and left it in a covered carport over the winter.


    Well this year when we launched it and tried to start it up it was stubborn. Finally we cranked it and played with the choke lever and whammo, it roared to life and then pegged the RPM gauge. I immediately backed off the choke (which I understand is just a way to throttle it in neutral) but the RPMs remain pegged at about 8K so I cut the power. I repeated this a few times and let the engine warm up a bit. It was running rough and the high RPMs were scaring me ... so I shut it down, popped the top and inspected everything.


    Once the cover was off it started at a low idle and was well behaved. We let it run for about 30 minutes and every so often would ramp the choke up and down, throttling it between 1K to 5K and back down without incident. Also tried turning it on and off a few times. Finally we applied carb cleaner and then inspected the throttle linkages. There was some play, but nothing seemed like it would be problematic.


    So we carefully took it out and drove it for about 30 minutes. It ran fine, turned around and came back. As we approached the Marina and I backed it off into Neutral, the shifter was a bit sticky. So I pushed it past the catch and as it hit neutral the engine decided to go full open throttle again. I jiggled the throttle to no avoid, and eventually had to cut the power with the key. Starting it back up pegged the RPM gauge even with the cover off this time.


    Upon starting the RPM was at about 3K, and it was rising about 100 RPM every few seconds. Eventually the gauge would bug out and I'd just cut it to be safe.


    With the engine off I observed the linkage movement as I throttled the shifter forward. There is a displacement of approximately 2", so I'm guessing externally visible cable and mechanical parts are not to blame. I'm just not able to see anything catch, or hang, or fail to retract.


    I lack the mechanical background that my Dad had, and seeking help from a Marina/Mechanic right now isn't looking good due to the months-long backlog of work they all have. Any thoughts on what I could try to resolve this issue?


    And when dealing with these kinds of engines, what guidelines exist for redlining them? Should I do everything to completely avoid it, or is some high RPMS for a minute or so while testing acceptable?


    Thank you for any insight you can provide me as I dive into learning about this engine!

  2. #2
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    15,543

    Default Re: 1980 Johnson 85hp stuck throttle

    You do NOT have a choke lever on the control box.------Motor is choked / primed by pushing in the key WHILE CRANKING I think.

  3. #3

    Default Re: 1980 Johnson 85hp stuck throttle

    Quote Originally Posted by racerone View Post
    You do NOT have a choke lever on the control box.------Motor is choked / primed by pushing in the key WHILE CRANKING I think.
    Yes, it is a bit misleading and has been discussed elsewhere on this forum. The startup lever is just as way to artificially increase the throttle while in neutral. Good for starting a cold engine. The push-to-choke/prime hasn't been working since we had a key mishap last year. And it hasn't been needed as the engine is generally quite easy to start. So that is an interesting thought. If the key mechanism was acting as though always pushed in, would that cause this kind of behavior?

    That is the one cable/function I hadn't traced to the engine and verified proper movement of.


    Thank you!

  4. #4

    Default Re: 1980 Johnson 85hp stuck throttle

    Alright so I took off the intake manifold cover, and sitting there touching the top butterfly valve was one of those thin red straws used on spray can nozzles. It seems impossible for that to have made it past the airfilter, and that manifold cover hasn't been removed since at least a year before my Dad passed away. What a bloody mystery.

    That being said, I am having trouble believing that thin little straw was somehow making the engine redline. Even if it was preventing the valves from fully closing, that would have been just a high idle. To be at 1500 RPM and suddenly jump to 8000 would require something forcefully opening the valves and keeping them there.

    So I removed the straw, buttoned the cover back up and was unable to get the engine to misbehave. But it did that before too. It would seem impossible to prove this is fixed without extensive testing.

    My testing included starting the engine which was nice and easy. Then I let it warm up at 1500 RPM, and took it down to 1000 RPM (lowest I saw) after 2 minutes. Then, tied to the dock, I did a few forward->neutral->forward->neutral and did not observe any jump in RPMs. The engine has, for the past few years, shuddered a bit while shifting gears. You need to make sure to push through the change or it can oscillate between them. Does this just sound like a loose linkage?

    I ran the engine at idle for 30 minutes, with 10-minute rests, three times. Every 5 minutes would put it in forward for 60 seconds, then reverse for 60 seconds looking for problems. I also thoroughly tested the throttle bar, taking it up to 3000 RPM and back down to 1000 RPM several times... taking care not to run the engine too long at high idle. Beyond this I'm not sure anything more could be done until the problem occurs again.


    If I happen to be out and the engine decides to redline while in-gear, does any method exist for cutting power other than removing the gas line and praying?

    Is it reasonable, or expected for good maintenance, to spray any kind of oil or cleaner on the open air intake manifold and butterfly valves?

    What is a good grease or oil to use on the linkages and throttle assemblies?



    Thank you!

  5. #5
    Join Date
    Feb 2001
    Location
    Central West Florida
    Posts
    14,595

    Default Re: 1980 Johnson 85hp stuck throttle

    The mechanic at the marina is responsible for the problem you encountered. When he winterized the engine, the long red plastic straw is actually the nozzle extension from the winterizing fogging spray can. How he could possible miss that flying off the can and into your carburetor is the mystery.

    When you take a engine to a marina to be winterized and stored... and it has been running perfectly... then in the spring you retrieve it and it runs as you explained in your first post..... think about that! No mystery as to who is responsible. Consider yourself lucky that's all he goofed on (hopefully)!

    Pertaining to racing the engine, either on a flushette... or in neutral with the rig in the water... DO NOT exceed 1500/1800 rpms and anything higher is risking a runaway engine..... the engine actually turns into a diesel and the rpms continue to rise higher with every passing minute... and turning the key OFF or even yanking the plug wires off does absolutely nothing.

    By the time you figure out what to do to stop the engine... connecting rods are flying out the sides of the crankcase.

    Also, with no offense intended.... what you removed has nothing to do with the intake manifold. That is called the "Carburetor Face Plate".
    We occasionally have questions. If you fail to answer, it may affect ours.

  6. #6
    Join Date
    Apr 2016
    Location
    barnegat NJ
    Posts
    3,144

    Default Re: 1980 Johnson 85hp stuck throttle

    Blocking airflow to carbs with big heavy rags would kill the engine as a last resort if the key doesn't do it.

  7. #7

    Default Re: 1980 Johnson 85hp stuck throttle

    Quote Originally Posted by joereeves View Post
    The mechanic at the marina is responsible for the problem you encountered. When he winterized the engine, the long red plastic straw is actually the nozzle extension from the winterizing fogging spray can. How he could possible miss that flying off the can and into your carburetor is the mystery.

    When you take a engine to a marina to be winterized and stored... and it has been running perfectly... then in the spring you retrieve it and it runs as you explained in your first post..... think about that! No mystery as to who is responsible. Consider yourself lucky that's all he goofed on (hopefully)!

    Pertaining to racing the engine, either on a flushette... or in neutral with the rig in the water... DO NOT exceed 1500/1800 rpms and anything higher is risking a runaway engine..... the engine actually turns into a diesel and the rpms continue to rise higher with every passing minute... and turning the key OFF or even yanking the plug wires off does absolutely nothing.

    By the time you figure out what to do to stop the engine... connecting rods are flying out the sides of the crankcase.

    Also, with no offense intended.... what you removed has nothing to do with the intake manifold. That is called the "Carburetor Face Plate".

    Well, it took me a few days to sort this mess out.

    We had not agreed to engine fogging last year, just lower unit winterization. We've not fogged the engine in 35 years of owning the boat, so why start now? But after some pressing they admitted they probably did fog it, but stopped short of owning the issue - "Oh, maybe it was the woman we fired last year who did it". Why does nobody stand behind their work? Negotiations will continue as our options for Marinas up here in Southern Ontario is limited. This time of year they all have 5x more work than they can handle, and finding competency with older engines seems to be getting harder and harder.

    Thankfully the engine appears to be operating well. We've been using it this past week and ran it through three tanks of gas without any problems. Just taking it one day at a time.

    The online Seloc manual I was looking at showed that as the cover to the intake manifold assembly, so that is what I called it. Still learning the lingo!

    Thank you for the input!

  8. #8
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    15,543

    Default Re: 1980 Johnson 85hp stuck throttle

    Where in Southern Ontario?

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