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Thread: Evinrude 31.8ci Mod Advice

  1. #71
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    Good evening. I have recently acquired a 1982 head as well. I'm wondering if I'll gain any compression just by simply by bolting it on. Did you use a certain head gasket? I've heard of a thinner version but can't find one.

  2. #72
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    Quote Originally Posted by PPRINT View Post
    The factory test wheel...

    I have an '81 35hp commercial engine that I recently picked up. I can tell the power head has been removed so I have no idea what all has been done to it.

    I do know it has the 1-3/8 dia carb that has the 1-1/8 venturi. It also has a power pack with no Rev limiter and very good compression.

    I ran it the other day in a 35 gallon barrel full of water with the factory test wheel.

    I let off the throttle at 7850 per the tiny tach in the interest of keeping the rods inside the block.

    Either I am using the wheel wrong, or it is not meant to hold the engine back much at WOT.

    Take that for what it is worth.

    Rob


    Sent from my SAMSUNG-SM-G900A using Tapatalk
    Im currently setting up a 25hp Evinrude with this carb and was wondering if you would tell me your jetting so I can have a rough estimate as a starting point for mine?

    My carb is off of a 70hp iof it matters.

    Thanks!

  3. #73
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    I am running a 59D jet.

    Let us know how that carb works out.

    Rob

  4. #74
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    Thanks PPrint.

    Any idea what your carb is off of?

    Do you have an idle jet? If so what size?

  5. #75
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    I purchased this engine used so I am not sure of the lineage of the carb. The motor itself is a 1981 25hp Commercial Engine (mistakenly identified as 35hp above in previous post).

    The carb does not have an idle jet. It is the adjustable needle valve style.

    Rob

  6. #76
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    Quote Originally Posted by PPRINT View Post
    The factory test wheel...

    I have an '81 35hp commercial engine that I recently picked up. I can tell the power head has been removed so I have no idea what all has been done to it.

    I do know it has the 1-3/8 dia carb that has the 1-1/8 venturi. It also has a power pack with no Rev limiter and very good compression.

    I ran it the other day in a 35 gallon barrel full of water with the factory test wheel.

    I let off the throttle at 7850 per the tiny tach in the interest of keeping the rods inside the block.

    Either I am using the wheel wrong, or it is not meant to hold the engine back much at WOT.

    Take that for what it is worth.

    Rob


    Sent from my SAMSUNG-SM-G900A using Tapatalk
    Generally above 7200 + or - is about it, a bearing cage fail is the likely reason. Not that an engine couldn't be built to go more but the weight balance alone in these stock is not extremely accurate. To move a moderate load at moderate speed and troll alot is the design trend.

  7. #77
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    I will just leave these here for discussion fodder.


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    Rob

  8. #78
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    These are the flow numbers of a stock reed plate versus a Yamaha 500CC jetski V reed block shown in the pictures.

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    Rob

  9. #79
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    That looks like a nice setup, but dual carbs seems like it would be a PITA.


    OK, I got my 1 3/8" carb on and it starts and runs but the idle jet is off.


    Iw will idle ok with the primer out on the first notch but when I take the primer off of the cold setting (First notch) it slowly revs faster and faster until it sneezes and quits.

    I know I need to go down on the idle jet, but how much or how many sizes?

    Im currently running a 40 idle jet.

    Do I go 39? 38?

    It doesnt run terrible but it certainly needs improving.

  10. #80
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    Quote Originally Posted by PPRINT View Post
    I will just leave these here for discussion fodder.


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    Name:  RT ISO.jpg
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    Name:  REED SIDE.jpg
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    Name:  LEFT SECTION.jpg
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    Rob
    The Mikuni slide carbs will probably perform better to start with. I made up a manifold to accept a 2 barrel carb from an OMC 85hp. Each barrel the same size as the stock single. Each cylinder draws from one barrel so it won't double the fuel requirement. It draws the same amount of air thru each barrel at half the pulse rate per barrel out of a common float chamber. No need to syncronize. This gave more mid range power but was not faster on top.

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