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  1. #1

    Default Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Hi all,

    I have an 1982 V4 115HP Johnson that has been running really well but yesterday it lost power as I was motoring at around 2500rpm it lost power and stalled. I noticed fuel coming out of the bottom carby and a quite a bit dripping from the bottom of the air silencer cover plate. I took it off and the petrol was running from the bottom carby's butterfly chambers and the two smaller brass rods. The carby itself seems ok and the float valve is working fine in the bowl. The primer was going hard and no fuel line leaks but once motor runs it begins to drip fuel from the bottom carby and just stalls. Could it be the reed valves? I posted a couple of pics.
    Any help or advice please guys? Thanks
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  2. #2
    Join Date
    Apr 2010
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    4,976

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Sounds like a bad needle & seat in the carb.

  3. #3

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Thanks Boobie. i hope it is as the reeds look ok from the outside. The motor was running well but lately was hard to start even though the primer solenoid was injecting fuel fine in each carby. I will redo the seat and needle as I have a 434888 carby rebuild kit. The silver round plugs are in the kit too but don't know how to change and the original ones seem fine still. Never had to rebuilt the carby before but keen to follow any advice you suggest thanks

  4. #4

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    My carbies do not have a removable plate on the top so I don't need the second gasket in the kit. The top is part of the main body. Float itself is still as new, not bad for 40 years old! What should I also inspect and change from the kit as never had to do a carby overhaul service before, only the usual maintenance. Cheers
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  5. #5
    Join Date
    Sep 2010
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    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Replace the float valves.------Clean out / replace all hoses between carburetors and fuel fitting on lower cowl.

  6. #6

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Quote Originally Posted by racerone View Post
    Replace the float valves.------Clean out / replace all hoses between carburetors and fuel fitting on lower cowl.
    Will replace float needle and brass valve racerone. Is there any chance it could be the reed valves? Can a float valve not seating perfectly cause so much fuel to drip? I have fuel line to replace those small length hoses also that go from the plastic fitting to the carby. All the others have been changed. What else from the kit should I change? I notice the needle on mine sits freely in the brass valve and that small wire curved attachment is not needed. Thanks again

  7. #7
    Join Date
    Sep 2010
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    20,950

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Yes , on a 40 year old motor the reed valves should be inspected / replaced.

  8. #8

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    So need to pull the manifold off? Sourcing new reed valves and a gasket for that age motor won't be easy here in Australia.

  9. #9
    Join Date
    Sep 2010
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    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    You are the one focused on the reed valves.------But they rarely fail.----Replace float valves and test run.

  10. #10

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Ok thanks a lot. Been doing too much reading and thinking Cheers

  11. #11

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Hi all, I replaced the float valve on the bottom leaking carby as I could only get one carby rebuild kit (439076) in stock. I cleaned all the carby with carby/throttle body cleaner and also took all 4 screws out for the low and high speed jets on the float bowl (mine has two screws on either side) and cleaned the passages and reinstalled them with O rings. I managed to get an additional float bowl gasket for the top carby, so I cleaned the top one too and reseated the float valve and needle. Both fuel lines leading into the carbies were replaced as I had replaced the others a few months ago. The primer bulb went hard, there were no leaks and it started straight away this time which was promising but it started to to do a sputter and continued to do so constantly both at idle and when revving it. There is spark to all 4 cylinders and I am at a loss as to why it keeps doing that.
    Any suggestions please?

  12. #12
    Join Date
    Sep 2010
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    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Compression test and post your results.----These motors are famous for broken piston rings.

  13. #13

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Will do that in the morning. Thanks

  14. #14

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Racerone, cold compressions are 109, 108, 105, 103. Never spluttered so regularly as it did after carbies cleaned. I am at a loss of doing anything wrong there.

    I doubled checked the way i put the new float, float valve gasket and pin in bottom carby and the float drop was between 22-28mm. Same thing with the top carby that i just cleaned out. Before reassembly I turned them up and down as is and there was no flow of air when upside down. Cheers
    Last edited by Snapper Fisho; 11-24-2020 at 05:53 PM.

  15. #15
    Join Date
    Sep 2010
    Posts
    20,950

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Those compression numbers would be LOW on my gauge.----And I have a good gauge. ----Are all throttle plates closed at idle ?

  16. #16

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Yes the plates are closed. I last did compressions on it 10 years ago and they were only 2-4 psi higher overall. My gauge is a ABW compression kit. Thanks

  17. #17

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Guys here is a google drive link of what it is doing....

    https://drive.google.com/file/d/1PWG...ew?usp=sharing

  18. #18
    Join Date
    Jul 2020
    Location
    Western Australia
    Posts
    56

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Flywheel key is a problem with them from what I have read,

  19. #19

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Could a fuel pump diaphragm be causing this? Cheers

  20. #20

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    No the flywheel is ok thanks

  21. #21
    Join Date
    Sep 2010
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    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    If flywheel tapers are clean and the nut is torqued to 102.5 FT-LBS the key is not a problem area.

  22. #22

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Could it be the fuel pump racerone?

  23. #23

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Put my finger behind it and there is a small wire protruding that moves in an out in line with the splutter. Maybe that's normal?

  24. #24
    Join Date
    Sep 2010
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    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Those fuel pumps are elegantly easy to take apart for inspection.---Just replace the diaphragm as it is just about the only thing that can fail.

  25. #25

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Great. Will try to get a diaphragm for it but might be easier to just get the whole fuel pump here.

  26. #26
    Join Date
    Sep 2010
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    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Myself I would never buy a new pump.----Repair kits is what I use !!

  27. #27

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Quote Originally Posted by racerone View Post
    Myself I would never buy a new pump.----Repair kits is what I use !!
    No luck sourcing a kit locally today. Can a faulty fuel pump show at low rpm and not a higher speeds?

  28. #28

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Measured warm compressions and they are higher, similar readings to those I got over 20 years ago, so I am really hoping now it is the fuel pump or could I still have a faulty carby?

    Cylinder 1: 112 psi
    Cylinder 2: 106 (this one had to have a heli-coil a few years back due to the thread wearing and felt the gauge thread didn't tighten as snuggly as the others despite O ring on it.
    Cylinder 3: 113
    Cylinder 4: 115

    Strangely motor has been running fantastic at high rpm and idling fine for so many years up until the bottom carby leak but was harder to start in the two times I used it prior to it stalling and leaking a bit of fuel the other day. There are no more carby leaks since servicing the carbies but it continues to run like the video clip I posted. I also replaced the spark plugs after the compression test a short time ago and no difference.

  29. #29
    Join Date
    Sep 2010
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    20,950

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    The bulb on the hose is a manual fuel pump.------So have your assistant operate it while the motor is running.----If there is no improvement / change in the way the motor runs there is nothing wrong with the pump on the motor !!

  30. #30

    Default Re: Johnson V4 115HP Outboard leaking fuel from the bottom carby

    Good to know. will squeeze the primer bulb first to see what happens when I run it later in the morning. Cheers

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