No top end on Johnson 25

Discussion in 'Outboard Maintenance' started by Andrewp, May 21, 2012.

  1. Andrewp

    Andrewp Going Solo .......

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    I finally had my first wet-test of my boat and engine. Boat is a 16' Fin and Feather, motor a '97 short-shaft 25hp remote Johnson. When I bought the motor I tested compression and got 125 psi on each cyl. When I had the engine set up I had tach installed so I could see what I would be running ....

    When I took boat out for first run, engine starts and idles fine, runs smooth. And acceleration is OK -- not great but I think part of the problem is the prop -- it's a 10" x 15". It does get up on plane. But boat feels like it's not making top speed. I did not have a GPS or speedo so I can only go by feel -- felt like we were making high teens. The weird part was that the tach was saying we were only making 2800rpm full throttle!!

    I was planning on taking boat back in to shop, but is there anything else I can do/check myself before turning it over to the pros?

    AP
     
  2. Brett

    Brett > PRO STAFF <

    Try a lesser pitch prop? :-?
     

  3. Gramps

    Gramps Living &amp; Dying in 3/4 Time

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    I was running an 13 pitch on my LT25 with a Merc. 25 2strk, but it was a light boat. You may check the tach settings to verify it is on the right pole setting. What model tach did you install?
     
  4. noeettica

    noeettica Well-Known Member

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    X2 15 sounds like a bit much ...

     
  5. Andrewp

    Andrewp Going Solo .......

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    Gramps -- don't know model (shop installed it) but when I spoke to the tech he said you are probably right about tach settings. he also said if I was only making 2800 rpm I would probably not be getting up on plane.

    So plan is to re-calibrate tach and try out a 10x13 prop.

    Thanks everyone for your comments.

    AP
     
  6. Punkrawqer

    Punkrawqer Hi, my name is Jon and I am addicted to Fishing...

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    Agree with pitch being lowered. A lesser pitch will raise your rpm's but lower you top speed.