Problems with Johnson 15 hp

Discussion in 'Bubba's Outboards' started by Raven Blayde, Jul 28, 2009.

  1. Raven Blayde

    Raven Blayde New Member

    Messages:
    320
    State:
    Kentucky
    I'm having an issue with a Johnson 15hp motor that is driving me nuts right now. The motor ran fine a couple of years back when my dad used it on his 14ft aluminum V-bottom boat. This summer, we put the motor on a 16ft fiberglass flat bottom John boat (a "Big John" model) and the motor runs fine at very slow speeds BUT it slips and jerks really hard if you try to go any faster. It won't even go fast enough to make any wake without this problem happening. First thing I tried was changing the tilt of the motor, but no luck there. 2nd thing I did was removed and completely disassembled the lower unit. I found that the "Clutch Dog" was worn a bit on the foward side, but not on the reverse side, so I flipped it around (putting the worn side on reverse). I reassembled the lower unit and refilled it to the proper level with fresh gear oil. I was pretty confident that I had found my problem, but I hadn't. The motor still had the same issue on the next trip out. Then I moved on to the prop and tried drilling 2 small holes on each side and inserting pins that reach all the way to the shaft (just to see if the prop was slipping under load). NOPE!!! The prop is not slipping either. Now I have no clue what to do next. Any advice?? Thanks in advance.
     
  2. Shimano_cat

    Shimano_cat New Member

    Messages:
    261
    State:
    North Caro
    Welcome to the BOC! Is the transom on the 16 foot boat taller than the 14 foot it was being used on? The shaft length of the motor could be to short for that boat.
     

  3. Cutbait101

    Cutbait101 New Member

    Messages:
    281
    State:
    south carolina
    Is the transom the same height on the big jon?just wondering if the motor might be too high?
     
  4. steve_b124

    steve_b124 New Member

    Messages:
    461
    State:
    south carolina
    Bobby,
    I don't know what year model you motor is, but it may have a rubber hub that holds the prop in place. It will act like a clutch and slip under load if not tightened properly or if worn. The first indication is usually slippage at higher rpm's. Had a 50 'rude that did this, I tightend the prop nut a couple of turns and used it for several months before it finally failed and had to be replaced.

    Older models had a shear pin instead of the hub. If the pin is sheared the prop will slip on the shaft. The prop \ shaft fit might be tight enough to turn the prop real slow, but slip under throttle.

    God Bless All,
    Steve
     
  5. Raven Blayde

    Raven Blayde New Member

    Messages:
    320
    State:
    Kentucky
    That's a good question guys (I never really thought to check). I'll check it out next time I'm at my dads house (that's where I keep my boats) and get back with you on that one. Thanks!!!
     
  6. Raven Blayde

    Raven Blayde New Member

    Messages:
    320
    State:
    Kentucky
    I checked it out last night and the transom on the boat the motor came off of was 15.5 inches. The measurement on the boat the motor is on now is 20 inches, which makes it sit up 4.5 inches higher than it was on the other boat. Would 4.5 inches make that much of a difference? If so, that could be my problem right there. I may try putting the motor back on the boat it came off of and take it for a ride this weekend (if weather permits) just to see what happens.
     
  7. Cutbait101

    Cutbait101 New Member

    Messages:
    281
    State:
    south carolina
    bobby you will need a 20 inch shaft motor,or you can cut the transom down on the boat.you need to cut it 5 inches lower then reseal the top of it.good luck mark
     
  8. Raven Blayde

    Raven Blayde New Member

    Messages:
    320
    State:
    Kentucky
    Thanks Mark! I'll see what I can come up with. Thanks to all for the help :big_smile: