77 70hp Evinrude low rpm problem

Discussion in 'Bubba's Outboards' started by 7mmmag1, Aug 18, 2009.

  1. 7mmmag1

    7mmmag1 New Member

    Messages:
    94
    State:
    Oklahoma
    It started a few weeks ago. My boat would run great at high rpms, but not so great at low rpms. It runs at low rpms but it sounds like its picking up a cylinder. I have good spark and good compression (135 on all). The rpms jump a few hundred rpms. It also has been fouling the plugs more often. I was thinking the fuel pump may be going out, and the vacuum leak is causing the jump in rpm. I sprayed cleaner in the carbs and put a new set of plugs in it and no difference.

    Any advice?
     
  2. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    Spraying cleaner in the carbs, does no good.

    If your primer bulb gets hard when you pump it up, the fuel pump's ok, or at least, the diaphragm doesn't have a hole in it.

    Do a proper carb cleaning, and check your gas for contamination.
     

  3. 7mmmag1

    7mmmag1 New Member

    Messages:
    94
    State:
    Oklahoma
    The primer bulb gets hard. I took the fuel pump apart yesterday and the diaphram seemed fine. I have run a few tanks of fuel through it because I thought it was bad gas too when it started acting up. Guess I'll monkey with the carbs today.
     
  4. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    If BobPaul says to clean the carbs, I'd clean the carbs. That is a man with a lot of knowledge.

    Sounds like there may be a partial blockage in the low speed jets. What bothers me is how it steadily gets worse...that sounds more like some type of electircal break down... like the coils are overheating, or the power pack. I know there are checks in the manuals to tell the condition of those items and I'd really give them a close look.
     
  5. 7mmmag1

    7mmmag1 New Member

    Messages:
    94
    State:
    Oklahoma
    It doesnt seem to really get any worse, I just havent found what is causing the problem and it is continuing to act up. If it was the coil I think it would either work good or work bad for more than a few seconds then switching. Hopefully tomorrow I can pull the carbs off and clean em. Thanks for the great advice so far
     
  6. johndeere nut

    johndeere nut New Member

    Messages:
    134
    State:
    oldham county,kentucky
    clean them good you may have water in the bowls mine had that and wouldnt idle make sure to adjust the carbs back to where they are synced to all open at the same time. get a manual and adjust the carb screws as it tells you be it 1 turn or whatever this will be a starting point you may have to fine tune after that because the carb settings in the book are for a new engine yours will have wear and will have to be compensated for when adjusting the idle screw