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Thread: 25hp 2 stroke 3 cylinder Johnson

  1. #1
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    Default 25hp 2 stroke 3 cylinder Johnson

    Question, I am brand new to the forum so I hope someone may be able to help out. I have a 1996 25hp 2 stroke 3 cylinder Johnson that I converted to as 35HP this winter. They made this exact same motor in a 35hp version, except it was a long shaft. We bored it, put 35hp pistons and 25hp carburator jets in it and a set of boyseen reeds. Used all OEM Johnson (OMC) parts in the conversion (except for the reeds). I am finally through the break in period (double the oil mixture for 15 gallons of fuel) and ready to see how's it is going to do on 50:1 and a new set of plugs. I use this boat for duck hunting, 1548 seaark semi-V aluminum flat bottom. Typical Arkansas duck boat set up. I do not race per say, well I guess we do race (sort of) at 4:00am in the morning on Arkansas public duck hunting land. I am competing with the 2 stroke 3 cyl. Suzuki's and Tahatsu's. I noticed they are "higher" geared, example 1.92:1 for the Tahatsu. My Johnson is 2.15:1, is there such thing as an aftermaket gear set for this model Johnson to get it closer to the Tahatsu ratio? Sorry to be so long winded.

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    Default

    I don't know about the gearing, but in your mentioning of motors you are contending with, you forgot the second most important motor aside from the Tohatsu mega and that is the 3 cyl yamaha 25.

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    Yeap your right! Those too! Hunted out of a boat last year (1648 War Eagle) with a 2 stroke 3 cyl Yami mod'd out. Fast!!

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    Thumbs up

    If you have bored the motor, more CI, check the plugs when you switch to the 50:1,
    You mentioned the 25hp jets. My .02

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    Fuelblndr,
    I put a new set in after the break in of 25:1 fuel. Is that what you meant by check the plugs?

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    Team Member proprider01us's Avatar
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    Default rejet

    I'm pretty sure he meant to check to see if your too lean. You may want to consider putting bigger jets in if you increased the bore size and made the intake track more efficient with aftermarket reeds.
    Just my thought.

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    We replaced the 25 hp jets with 35 hp jets.

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    Team Member capnzee's Avatar
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    It is still a good thing to check the plugs soon after you have made changes to the carburetion, ignition etc. By checking the plugs you will see exactly how the engine is running in the combustion chamber. Remove the plugs and look at the gap end. If the plugs are white/gray (chalky) looking you are running too lean. If your plugs are black and oily looking, you are running too rich. If your plugs are brown, you are running pretty close to where you want to be. Look out if your plugs are chalky white!, in fact I would not run it again until you "richen" it way up.

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    Just checked the plugs I pulled out yesterday and they are brown in color.

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    Default OMC mini loop triple

    Quote Originally Posted by speedfreak View Post
    Just checked the plugs I pulled out yesterday and they are brown in color.
    http://www.boatracingfacts.com/forum...t=7707&page=17

    Hey Speedfreak, In case you hadn't seen this before. I built this 35HP OMC triple for my son's 11' runabout. It runs 55MPH at 5750 RPM on the A15 racing gearcase. If you need to run a shifter, contact Ron Hill for a racing prop.

    Tim

    BTW: You'll want to get 35HP carbs and open up the airbox.

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