1980 25hp Johnson carb question

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

  1. 4bratsdad

    4bratsdad Member

    Messages:
    241
    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
     
    Catpaw likes this.
  2. Toneyd

    Toneyd Well-Known Member

    Messages:
    212
    State:
    oklahoma
    Name:
    Toney
    Wasn't that on the 9.9hp?
     

  3. 4bratsdad

    4bratsdad Member

    Messages:
    241
    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 Member

    Messages:
    35
    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:
    241
    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
     
    Catpaw likes this.
  6. tommeboy

    tommeboy Active Member

    Messages:
    307
    State:
    Iowa
    Name:
    Thomas
    You also need the intake and reed cage to modify the motor to 35. Well 30. The 35 was changed to a 30 when they started to rate the motors at the prop.
     
  7. Fishon1213

    Fishon1213 Member

    Messages:
    35
    State:
    Illinois
    Name:
    Al
    Bottom line.
    20mph is pretty respectable for that boat/motor. The bad news is that it tough to find anything larger than a 25hp in short shaft. I've always wanted a faster boat but with a flat bottom you usually end up cruising around 20mph anyway, unless the water is glass. The fish don't care how fast your boat goes.
     
  8. 4bratsdad

    4bratsdad Member

    Messages:
    241
    State:
    illinois springfield area
    According to the plate and number stamped on freezeplug it's a 1980 model
     
  9. 4bratsdad

    4bratsdad Member

    Messages:
    241
    State:
    illinois springfield area
    Update I had to replace waterpump and had problems with float sticking so I took it to a shop , the mechanic upgraded the carb to what he called 28hp larger carb it runs better planes quicker but still not getting over 20 mph I found out pods were full of water hairline cracks on each , drained that, almost 10gal , filled with foam & moved the batteries and fuel to the front , it sits higher in the back I have prop ordered it had a 12 pitch , the highest for this motor , but it was tore up , the mechanic had same motor on his boat really suggested I go with a 11 so I'm gonna try that , had hard time locating props for this model on eBay ,the dealer wants over 120 and week wait it's not a pin drive and not through hub , so I broke down and let them rob me hopefully it helps
     
  10. 4bratsdad

    4bratsdad Member

    Messages:
    241
    State:
    illinois springfield area
    I was told these motors do not have reeds , I've modified reed cages for dirt bikes , I found out this motor had 2 options on carbs a 25 and 28 hp , I bought the 28 from a trusted mechanic and he installed it but it's no faster, just runs a whole lot smoother , my problem now is I cannot find a prop for this motor it's oddball nobody seems to have it or aren't able to get it
     
  11. tommeboy

    tommeboy Active Member

    Messages:
    307
    State:
    Iowa
    Name:
    Thomas
  12. BBK

    BBK Active Member

    Messages:
    229
    State:
    Iowa
    Name:
    Kevin
    20mph in that boat with a 25 is very respectable. I doubt youll see more than 23-25 even if you get it to 35hp powerhead.

    Oh and as far as motor height, you want the cavitation plate (fin) to be at the surface or slightly above it WHEN THE BOAT IS ON PLANE AND TRIMMED, it will be way below when just sitting in the water.
     
  13. CatDawg71

    CatDawg71 Active Member

    Messages:
    154
    State:
    georgia
    Name:
    Brad
    I had a 15' Fisher marine with a 25 Evinrude that would go about 22 mph fully loaded. 1985 model that was light. You may get a few mph from a different pitch prop but I agree your close to what it's performance will be. When my motor got about 30 years old, had to replace wiring as insulation had deteriated. Good luck with it.

    Sent from my SM-G920V using Catfish1 mobile app
     
  14. 4bratsdad

    4bratsdad Member

    Messages:
    241
    State:
    illinois springfield area
    Yeah I guess I'm not gonna get any more out of it ,I ordered a prop , I'm looking for good used 40-50 hp now
     
  15. Fishon1213

    Fishon1213 Member

    Messages:
    35
    State:
    Illinois
    Name:
    Al
    If you really need more speed/power then you should modify the transom or get a jackplate to accommodate a long shaft motor. Anything over 25hp is tough to find short shaft, once you go to a long shaft motor your options open up immensely.
    Fwiw speed is cool but not usually important, as long as you can get on plane live with it. Bigger motor usually means more complicated and expensive repairs. 25 johnyrudes are fantastic, I miss mine. The main reason I moved on was to get power tilt.