1991 Johnson 70hp 2-cycle

Discussion in 'Outboards' started by cessna402, Apr 9, 2011.

  1. cessna402
    Joined: Apr 2011
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    Location: Concord, NH

    cessna402 New Member

    Hi I have a Johnson 70hp that has been giving me a fit while starting.
    It will smoke like I'm spraying for bugs for a minute or two the clear
    up and run fine.

    When I go to start it sometimes it will try to start then not start, I have
    to take the cover off and turn the auto-choke (red) cam to the complete opposite side. For some reason it will start! When I attempt to start
    it hours later it will try to start then not start, unbelievably I turn the auto-choke (red) cam to back to where it was "on the opposite side" and it starts.
    When I push in on the key th auto-choke clicks as if it is working.

    HOW CAN THIS BE POSSIBLE? Foe whatever reason it works. It still runs like crap for a minute or two, regardless. Any ideas.


    This past summer the carb bowls were filling with 2-cycle oil so I drained them and disconnected the oil tank, plugging the inlet. I think my big fuel line may be cracked allowing air to leak causing the carb bowls to fill w/ oil.
    It seemed like it help, but it is still not right and gives me fits.


    This spring out of the water I replaced the white fuel filter and replaced the water-pump. Leaving the auto-choke (red) cam in the detent position pushing in on the key it started. Seemed alittle better, I dont know.
    This summer will tell.

    The big mystery to me is why does moving the auto-choke (red) cam from opposite sides at different times allow it to start as described above?

    I always thought that with the red cam in the detent was auto-choke position
    is this the case?


    Thanks Dano
     
  2. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    If you turn the lever to point away from the choke solenoid then any residual pressure in the fuel line will run straight into the reeds, ( the injection port is right at the back of the carbs)
    If you run the engine with the lever this way the fuel pump pressure will just pump tons of fuel straight into the engine.
    Sounds like you might have a blockage in one of the nozzles they are about a 010" hole.
    You can unscrew the fittings and clean them.
    It may be that you are flooding one cylinder with fuel but the others are dry?

    From about 2000rpm in neutral the engine will drop to 1000 with the choke on if all 3 are clean and working.
    You couldnt trust that the solenoid clicking means fuel is going through it.
    Pull the hose of and see what happens when you both turn the lever and with it in the auto postion and press the key.
     
  3. cessna402
    Joined: Apr 2011
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    Location: Concord, NH

    cessna402 New Member

    Thanks for your thoughts.

    I understand I should have the red-cam in opposite position, fully away from the detent.

    Is this not in the manuel full-choke position.

    I am assumng you mean after I start the motor in the detent position.


    Dano
     
  4. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    the lever should be pointing along the solenoid for normal use i.e aft
    The solenoid is just an electrical switch that when you press the key for choke allows fuel pressure to go straight into the reads from behind the carbs.
    If you had a flat battery and wanted to pull start your engine, turning the lever forward manually opens the valve so when you squeeze the primer bulb fuel will go into the engine for starting then you turn it off meaning back to the normal postion
     
  5. freemdav
    Joined: Apr 2011
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    Location: VA

    freemdav New Member

    I'm having the same issue on a 95 Johnson 225. Still doing some R & D but It may be that the OIL tank vent is clogged causing pressure to build up in the oil tank forcing oil into the carbs.
     
  6. freemdav
    Joined: Apr 2011
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    Location: VA

    freemdav New Member

    Can you let me know if fixing the cracked fuel line fixed the problem. I found out that if the fuel line is letting air in, it will cause the VRO pump, to pump more oil then fuel in to the carbs. I may have an air leak and need to replace the fuel line. Thnaks
     
  7. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    yes air leak will make the vro pump like crazy and every extra stoke means it pumps oil and pressurised oil tank will force oil into carbs at rest
     
  8. Frosty

    Frosty Previous Member

    An air leak will make the pump pump like crazy?

    Can you explain the mechanics of that please?
     
  9. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    No prob
    the oil pump ( piston style) is on a shaft that connects it to the diaphram in the fuel pump but with a lost motion connection. ( push pull, all in one assembly)
    The lost motion part ie a big end with no bearings if you like, means small pump stroke means very small oil pump stroke.
    Pump is designed to be calibrated so that a certain stroke of diaphram versus revs will cause the correct stroke of oil.
    Pump will obviously go faster with more revs and the fuel consumption per oscillation will determine how big a stroke it will do and hence how much oil it will pump.
    So they run from about 150:1 to 40:1
    Now if the pump is pumping air and fuel it will do a bigger stoke and hence pump a large amount of oil for a small amount of fuel.
    does that make sense?

    In the old days the diaphram pump didnt care if it pumped a bit of air as it just vented out the carby bowl vent
    Cheers
     
  10. Frosty

    Frosty Previous Member

  11. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    Thats not removing it that just stopping the oil going into the pump and capping the lines so you then need to add oil to the fuel
    BRP also sells a fuel pump without the oil pump.
    Never seen a pulse line break its a high quality piece of hose but yes less pulse less fuel so less oil
    The oil pump is not connected to the crankcase only to the fuel pump via a plunger
     

  12. Frosty

    Frosty Previous Member

    Pulse pumps are old stuff. Yes you remove the function and fil the tank with a mix of your choice. Racers did it 1/4 of a century ago.

    Suzi I think was the first with their 80 over 35 years ago. It was to orisky to allow the pump an important function in those day, It wasn't trusted, and in some cases it was a valid reason.
     
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