1980 25hp Johnson carb question

Discussion in 'Bubba's Outboards' started by 4bratsdad, Jul 12, 2017.

  1. 4bratsdad

    4bratsdad Member

    Messages:
    235
    State:
    illinois springfield area
    IMG_1896.PNG IMG_1916.JPG I just recently purchased a polarkraft 18/52 jonboat with what I believe is a 1980 Johnson 25 the motor seems to run & idle fine but it's slow ,I'm not sure of the pitch on prop ,I cannot find a stamp ? I was told on these older2 stroke Johnsons you can simply change the carb to get about 35hp does anyone know if this is true ? My boat has aluminum floor and pods on the back no heavy extras like wood or live-well, it only gets up to 20mph on calm water , the transom was cut down and modified for a short shaft motor , I was always told the cavitation plate should be close to level with bottom of transom ? On this boat it's about 2-2 1/2 " below the transom , was wondering if that might be part of it ? This is my 1st 18 jon , but I'm use to speeds of 25 -32 with mid 90s Johnsons Nissan , and 99 evinrude , and hit 35mph with a Suzuki that should have never sold , I've learned to keep the boat light as possible & I remove any wood waterlogged foam etc , just wondering if I can do much with this motor or should I just jump up to a 40-50hp ? I'm afraid if I go bigger it will sag more, I run through a lot of shallows ,mostly river fish , I can get through about 12" now but found I can run a lot shallower with some weight on the front ,in the process of relocating batteries and fuel tank to the front, so I'd love to keep the 25 for rear weight reasons if I could just get a lil more out of it ,something noticeable ? Thanks for any tips ! I will try to add pic of the motor
     
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  2. Toneyd

    Toneyd Well-Known Member

    Messages:
    180
    State:
    oklahoma
    Name:
    Toney
    Wasn't that on the 9.9hp?
     

  3. 4bratsdad

    4bratsdad Member

    Messages:
    235
    State:
    illinois springfield area
    I've always heard the 9.9 could be converted to 15 yes , but recently heard the 25 can be bumped up with 35 carb , I've done it on quads and 3 wheelers and it did make them scream
     
  4. Fishon1213

    Fishon1213 New Member

    Messages:
    5
    State:
    Illinois
    Name:
    Al
    You can get more power with a 35 carb/jets.....But
    Looks like a heavy boat, might be all you can expect. That motor is likely mid 70s from the lower unit design. The hub in the prop might be slipping, have the prop rebuilt. A hydrofoil could make a huge difference as well. Those motors are easy to work on, rebuild carb if needed and make sure lean/rich and linkage is adjusted correctly.
    Imho, 2stroke johhnyrudes aren't the fastest thing out there but they are simple, reliable, easier and cheaper to fix than other 2stroke competition.
     
  5. 4bratsdad

    4bratsdad Member

    Messages:
    235
    State:
    illinois springfield area
    I don't get it , I was taught that the cavitation plate should be even with bottom of boat or up , within 1", varified this from local boat shop , because I saw mine was down too far , so i built a jackplate and raised it 2 1/2" , and took it out for a test and it wouldn't plane it was sucking air and I could hear the exhaust like when the motor is out of the water , it was sucking air , I don't get it ,unless having pods would mean you have to lower motor , my transom is 16", I know I have a 9 pitch prop which is the smallest /highest rev , im thinking of stepping it up to a 11 pitch , I'd love to have a 40-50hp on it but would rather run shallow water at 20 then loose 12" of floatation in the back for the bigger motor
     
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