Idle's fine with muffs, no so good in water

Discussion in 'Bubba's Outboards' started by SCcatman, Jul 2, 2009.

  1. SCcatman

    SCcatman New Member

    Messages:
    64
    State:
    South Carolina
    1999 Johnson 40HP model J40PLSSM.

    When I hook the muffs to it and let it run it idles perfect, no sputter or anything. But when In the water it will idle and sometimes shut off, it fires right back up but its like it wants to sputter off, I am able to push the choke in for a second and it smooths back out, or give it a little throttle so the carbs are open a bit and it runs like a top. Why will it run perfect on the hose but idle bad in the water? Does the back pressure of water affect the idle? I guess the hose pipe doesn't put any back pressure on it? Could it just be a rpm issue when back pressure is applied? Would increasing the RPM's fix it? any help is appreciated.

    Thanks
     
  2. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    There are two distinct possiblilties. Something is blocking the exhaust. When on muffs, the engine normally exhausts through the propellor. When in the lake, you have back pressure by the water. Second, the final adjustments on the carbs should be made with the boat in the water, not on muffs. Makes a big difference in the way the motor preforms.
     

  3. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    So many things to check, is why good mechanics earn thier pay.

    The previous post is correct. Carbs are set with the boat in the water, in gear, and unrestrained. That means in motion:wink:

    Take someone with you.
     
  4. smokey

    smokey New Member

    Messages:
    1,876
    State:
    Tennessee
    do you have water in your gas? when the muffs are one it, its not moving gas stays seperated from water,when your on the water your gas gets mixed up with water. and spits and sputters.
    smokey
     
  5. SCcatman

    SCcatman New Member

    Messages:
    64
    State:
    South Carolina
    What is the proper adjustment on this model? anyone?

    smokey, I am not sure if I understand what you are saying. If water is in the gas it will be used when the engine is running, whether in the yard or on the water. What am I missing.
     
  6. Johnny B

    Johnny B New Member

    Messages:
    253
    State:
    illinois
    he's probably just saying the water and gas would get mixed up from the wake or waves but I wouldn't say that is correct I would check the exaust!:wink:
     
  7. SCcatman

    SCcatman New Member

    Messages:
    64
    State:
    South Carolina
    ok another noob question, where exactly is the exhaust? and when you say check it is that done from inside the cover?
     
  8. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    There are basically two exhausts on the motor. One is the two small holes on the upper portion of the lower unit where we look to see if the motor is "peeing". Thats actually two exhaust ports. The other is through the center hub of the propeller. When you have the motor running on muffs, the center hub is not restricted. When you put the motor in water, it covers a good portion of the lower unit, including the propeller. That is where you would get the back pressure.

    As to adjustments of the carb, you need to get a manual. Check your local library for your make and model as they normally have a lot of reference material, or can get it from a major library for you. That failing, you need to buy a manual. They are just as important to boating as a horn, lights, fuel tank, anchor, etc.
     
  9. SCcatman

    SCcatman New Member

    Messages:
    64
    State:
    South Carolina
    Thank you for explaining that. how can i tell if its blocked though? the 2 holes you are referring to on the upper part of the lower unit "pee" water fine. I guess i need to remove the prop to inspect that area?

    If those area's are free is my next step the carb adjustment?

    I have a manual ordered. thanks
     
  10. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Gosh, know you've gone and asked one humdinger of a question. I think the best answer is to drop the lower unit. Once it is separated, you can see the exhaust tube up to the exhaust manifold, and from the top of the lower unit to the prop. Any blockage should be visible - I would think. If it is peeing, I would think that portion of the exhaust is okay. Mud daubers do have a tendency to build a nest in those holes, so you should be able to check them with a soft wire and flash light. LOL
     
  11. SCcatman

    SCcatman New Member

    Messages:
    64
    State:
    South Carolina
    Thanks, lastly, can I drop the lower unit without draining the oil?
     
  12. CatHunter24

    CatHunter24 New Member

    Messages:
    715
    State:
    Dayton, Ohio
    they always say you must drain the lower unit before dropping it but when we dropped my Merc's to change the water pump impeller we didn't have to. Not sure about your particular application though.
     
  13. SCcatman

    SCcatman New Member

    Messages:
    64
    State:
    South Carolina
    Would the throttle cam and linkage being out of alignment cause this idle issue?

    I got my service manual and did a sync and link adjustment on the throttle rod/cam etc. It was out of align by about 1/2" based on the alignment marks on the cams. I got all back to factory specs but haven't had a chance to run it.

    Just curious if this could be my idle issue?
     
  14. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Definitely.