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  1. #1

    Default 1986 Johnson v4 looper

    Hello this is my fist post here I have a question about my 1986 Johnson v4 looper 140 it currently has 95 psi on all 4 cylinders I have rebuilt the carbs 2 times and taken them off 2 times more to clean again I have no gas leaks or air leaks my reed valves are all seated but Everytime I take it to the water it runs great for about 10 mins wot then boggs down and only runs about 5mph back to dock and runs ruff after bogging down does anyone have any suggestions for what else to check for? Thanks

  2. #2
    Join Date
    Apr 2010
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    5,327

    Default Re: 1986 Johnson v4 looper

    Do a cylinder drop test on it when it acts up and that may tell you something.

  3. #3

    Default Re: 1986 Johnson v4 looper

    Quote Originally Posted by Boobie View Post
    Do a cylinder drop test on it when it acts up and that may tell you something.
    Ok I have to buy a tester to do that thanks for the advice Boobie

  4. #4
    Join Date
    Nov 2005
    Location
    Mt. Zion, Illinois,
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    1,170

    Default Re: 1986 Johnson v4 looper

    You could have an ignition component failing once it's heat soaked and the drop test Boobie suggested will confirm that. Run the engine until it acts up then do the test.

    Also, you might want to look into your fuel tank. It's possible your tank vent is clogged or anti-siphon valve is sticking which creates a vaccuum in the supply line. I'd lean more toward the failing ignition component, but the fuel system is free to check.


    KJ

  5. #5

    Default Re: 1986 Johnson v4 looper

    I checked all the fuel lines and vent line then I pulled the supply tube from the tank and it was clogged with sealant I have no idea how that could have gotten in there I really hope thats what is was the entire time now I have to wait till next week when the reed and head gaskets get here and I'll do a run and see any tricks to get the flywheel off because it's on there sooo tight

  6. #6
    Join Date
    Nov 2005
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    Mt. Zion, Illinois,
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    1,170

    Default Re: 1986 Johnson v4 looper

    Quote Originally Posted by Jamesk83 View Post
    ... supply tube from the tank and it was clogged with sealant...I have to wait till next week when the reed and head gaskets get here and I'll do a run and see any tricks to get the flywheel off because it's on there sooo tight
    Let's take this step-wise. For the Cylinder drop test you only need a pair of plyers with rubber coated grips. The reed and head gaskets were most likely unneccesary

  7. #7

    Default Re: 1986 Johnson v4 looper

    I just wanted to know for sure that the Reed valves are good and head gasket just wanted to know for sure. And with coated pliers are you saying pull the plug wires from the plugs while the engine is running after it is acting up?

  8. #8
    Join Date
    Nov 2005
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    Mt. Zion, Illinois,
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    1,170

    Default Re: 1986 Johnson v4 looper

    Quote Originally Posted by Jamesk83 View Post
    I just wanted to know for sure that the Reed valves are good and head gasket just wanted to know for sure. And with coated pliers are you saying pull the plug wires from the plugs while the engine is running after it is acting up?
    Yep, while its running (and acting up) you pull a spark plug lead and listen to the engine to see if there is a difference. If the engine wants to die that cylinder was fine. If it keeps running the same (badly) when you pull the lead then it means that was a dead cylinder.

  9. #9

    Default Re: 1986 Johnson v4 looper

    Quote Originally Posted by kevinj View Post
    Yep, while its running (and acting up) you pull a spark plug lead and listen to the engine to see if there is a difference. If the engine wants to die that cylinder was fine. If it keeps running the same (badly) when you pull the lead then it means that was a dead cylinder.
    Ok got it thanks kevinj I'll try that when I take it out next Saturday hopefully I do not have to do it and it was just the clogged pick up tube fingers crossed ����

  10. #10
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    Apr 2010
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    Default Re: 1986 Johnson v4 looper

    What ever happened ????

  11. #11

    Default Re: 1986 Johnson v4 looper

    Ok put everything back together took the boat out today for a test and it ran great at about 8 miles of 3/4 throttle I slowed down turn back for the dock an it wouldn't get back up to wot just under. even at full throttle it wouldn't get to wot and if I did push it to full throttle it would bog so it tried the choke for a second and that bogged it down as well but other than that it runs ok so I'll take it back out tm or Monday and test the timming. I got so overwhelmed that it was running pretty good i forgot I even had the timming light with me
    Last edited by Jamesk83; 08-28-2021 at 09:42 PM.

  12. #12
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    Default Re: 1986 Johnson v4 looper

    Read post # 2 again !!

  13. #13
    Join Date
    Nov 2011
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    tennessee
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    Default Re: 1986 Johnson v4 looper

    It not the timing setting in degrees, but could be the timer baser or timing arm not fully advancing.
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  14. #14

    Default Re: 1986 Johnson v4 looper

    I stopped this morning at HD and grabbed some clear lines to see if theres air getting in and when I started it this morning the main fuel line coming from the pump down to the manifold splitter is about 80% air and only 10% fuel

  15. #15

    Default Re: 1986 Johnson v4 looper

    Ok I took the boat today after installing all new full lines and fuel pump and still did the same thing then I did the cylinder drop test and when pulling bottom plug on port side made no difference in engine idle I could clearly see arking on the top coils so I cleaned the grounds on them and it stopped arking but I can hear electrical popping tho I'm going to order 4 new coils to be on safe side and change them all together... What do you guys think???

  16. #16

    Default Re: 1986 Johnson v4 looper

    Out testing this afternoon and found one completely bad coil that has the arcing and one that has very weak intermediate spark so I used ones from port side and they pass the spark test with strong white spark

  17. #17

    Default Re: 1986 Johnson v4 looper

    Update

    I replaced all the coils and took out this morning it ran soooooo good we took a 15 miles trip it was so nice being able to just go. On the way back to the ramp at full throttle it would slightly jump in rpms making us go from 30 to 36 mph and if I found the sweet smooth running spot it would run nice at 4300-4500 rpm wot any ideas to why the rpms and speed would jump like that? Like it has more power it's just not getting there

  18. #18
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    Default Re: 1986 Johnson v4 looper

    How old are the spark plugs ??

  19. #19

    Default Re: 1986 Johnson v4 looper

    The plugs 2 months old

  20. #20
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    Apr 2010
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    5,327

    Default Re: 1986 Johnson v4 looper

    Put a timing light on each cylinder when it's acting up and look into for black spots. If you spot some that's the cylinder that's acting up.

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