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  1. #1
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    Putting bigger carbs on a 40 hp yamaha

    I have a 1989 yamaha 40 hp and I was thinking about putting bigger carbs on it. I was wondering if any of y'all could point me in the right direction on going about this. I'm some what new to this but I do have a little knowledge about outboards. I know I will need to redo the exhaust to make it run right but what else is there to it? And what year model carbs will bolt up to my motor? I was talking to a guy the other day and he said something about putting 70 hp carbs on it, can this be done or will it need a new head and everything for it to run right?

    Thanks!

  2. #2
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    Hydro Tech makes a tuner kit for that motor..

    there claims seem a bit high but worth looking into..

    http://www.shop.hydrotecmarine.com/p...2&categoryId=4

  3. #3
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    Can you mod the carbs you have? Is the throttle plate the smallest dia. of the bore.
    13' Biel tunnel AKA "Flight Risk"
    13" Modified Yamaha V4 - 101 mph

    21' Paramount
    Mercury 300 Promax

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    Quote Originally Posted by Mr. Demeanor View Post
    Can you mod the carbs you have? Is the throttle plate the smallest dia. of the bore.

    I could put larger jets in it I believe. But I don't know about the throttle plate

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    Just wondering if they can be bored. Mine are 34mm stock but the dia. at the butterfly is 39mm. The 34mm is ahead of the butterfly choking it down. We bored them to 36mm and did some mods to the throttle shaft reducing its profile. Picked up 150-200rpm on my modded Yamaha 130.
    13' Biel tunnel AKA "Flight Risk"
    13" Modified Yamaha V4 - 101 mph

    21' Paramount
    Mercury 300 Promax

  6. #6
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    70 carbs are a big bore version of the 40/50 carb...otherwise they are pretty much identical. To see any real performance gains you will need to change the tuner. The 40 tuner is very restrictive so you'll need the pro50 tuner at the very least.

    You can change the tuner and I think jetting and make it a 50 pretty easily.
    '08 SRV
    Yamaha 3.1 Phase III


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    Quote Originally Posted by DoktorC View Post
    70 carbs are a big bore version of the 40/50 carb...otherwise they are pretty much identical. To see any real performance gains you will need to change the tuner. The 40 tuner is very restrictive so you'll need the pro50 tuner at the very least.

    You can change the tuner and I think jetting and make it a 50 pretty easily.

    What year model carbs will bolt straight up to my motor? And what do you think the best tuner would be?

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