Where's my RPM's?

Discussion in 'Bubba's Outboards' started by Catwagon, Apr 21, 2007.

  1. Catwagon

    Catwagon New Member

    Messages:
    125
    State:
    Justin, TX
    I have a '71 25 horse Johnson and it's giving me fits.

    I've replaced the impeller, carb, head gasket, fuel pump and fuel lines and even bought a new plastic tank to assure there would be no trash. (And yes, the fuel is brand new and properly mixed.)

    Problem is, it won't "open up" and insists on running at no more than low rpm which only gives me a top speed of about 5 mph. It'll run all day like this no matter what I do to it or how hard I twist the handle.

    The weird thing is if I put it in reverse and give it some gas then the motor will rev up to full normal speed like nothings' wrong with it. What gives?

    By the way, it won't start at all unless I put it in forward and twist the trottle open as far as it will go.
     
  2. dougc

    dougc Active Member

    Messages:
    1,711
    State:
    Independen
    Sounds like it could be a throttle linkage/timing advance problem.
     

  3. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    Take the hood off, work the throttle and see what's happening. Nothing like a visual inspection.
     
  4. Catwagon

    Catwagon New Member

    Messages:
    125
    State:
    Justin, TX
    Everything seems to be working flawlessly. The arm where you set the carb timing rolls and opens the throttle plate like it should, the throttle plate opens nice and smooth. The choke works perfectly and stays out of the way when it's not needed. Towards the right rear of the engine, the arm that advances the magneto progressively moves everything ccw the direction it supposed to go smoothly until it bumbs into a limiter on the left side of the engine as I open the throttle.

    In short everything works perfectly mechanically. I have an originally 71 Johnson factory shop manual that I go by and according to it I'm supposed to be ship-shape. But, the trouble shooting section doesn't cover running at low rpm only so I'm completely stumped.
     
  5. psychomekanik

    psychomekanik New Member

    Messages:
    2,534
    State:
    Illinois
    go through your carb settings, and timing procedure in the maintenance settings in the shop manual again. i'm not a marine mechanic. but i know if you make an adjustment out of order. it can screw up the rest of the adjustments. i'd really study that manual. maybe there's something you missed. the info is all there, it's just a matter of finding it.
     
  6. psychomekanik

    psychomekanik New Member

    Messages:
    2,534
    State:
    Illinois
    also, might it be something in the lower end seizing or binding in forward and not reverse? something to think about....
     
  7. Catwagon

    Catwagon New Member

    Messages:
    125
    State:
    Justin, TX
    I'll do that. My understanding of carburetion and timing is not one of my strong points so I could have easily missed something I guess. Thanks Mark, maybe I won't have to shoot it.
     
  8. turtle1173

    turtle1173 New Member

    Messages:
    611
    State:
    Mayfield, KY
    Perhaps I'm missing something but it sounds like it's only hitting on 1 cylinder. This is a two cylinder motor, I'm assuming. Does this motor have points? Seems to me like they need a cleaning or replacement.