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  1. #1
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    Yamaha carb swap 40hp with 50 or 70 carbs butterfly arm differences???

    Hi everyone,
    I have a late 1989 40hp yamaha. I wanted to put a set of 50hp or even 70hp carbs on. I picked up a set of 50hp carbs off a 2000 model and the arms that open and close the throttle are bigger. I ended up putting them on but i cant get wide open throttle. Is the difference because im going to a 50hp carb or is it because im going from a 1989 to 2000 model??? The carb bolts on fine but the linkages dont fit properly. While im at it, if its just due to the newer carby, could i bolt on a 1989 70hp carb or would the butterfly arms be different too? Thanks heaps
    riverrat321

  2. #2
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    post 95 they are a push to open.
    the 89 70 carbs will bolt on with no mods
    Aquarius Inflatable Yamaha 70 EFI
    24 Skater Twin 3.0 300x copies 113mph so far
    954-861-1611

  3. #3
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    Hi Berg969,
    Thank you for your reply. Are the control arms for the throttle butterfly the same size movinf from 40 to 50 or 70? Just want to make sure I will be able to get wide open throttle etc. my motor is tiller steer and has the shorter tiller arm on the side and gears on the side. I had to get an older motor because the newer ones have a very long tiller arm that is centred.
    oh I did a search on the forum last night. There was a picture of a short shaft 70 you had for sale. Looked great!
    Riverrat321.

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    yeah the 40/5-/60/70 round carbs or early square bowls are all the same just different bore size.
    also all the tillers are interchangeable
    Aquarius Inflatable Yamaha 70 EFI
    24 Skater Twin 3.0 300x copies 113mph so far
    954-861-1611

  5. #5
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    Great, thanks for that. If I put 70hp carbs on a stock 40hp would I get decent performance gains? I can get a 50 exhaust tuner as well. Would like to get a bit more power than, say a 50 tohatsu.

  6. #6
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    yeah put the 50 exhaust cut an inch off of it and remove the silencer can in the mid.
    Aquarius Inflatable Yamaha 70 EFI
    24 Skater Twin 3.0 300x copies 113mph so far
    954-861-1611

  7. #7
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    Ok I have a set of 70 carbs and they bolt up ok. I havent done the exhaust yet. Will it be ok to run the motor with these carbs and leave the standard oil injection hooked up?
    Thanks for your help.
    riverrat321.

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    should be fine. maybey a bit rich with the 40 exhaust
    Aquarius Inflatable Yamaha 70 EFI
    24 Skater Twin 3.0 300x copies 113mph so far
    954-861-1611

  9. #9
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    Thanks heaps for your help with that. Much appreciated.

  10. #10
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    Hi again, just curious, my engine does not run as smooth now at low rpm and it is hard to get it to idle slowly, is this usual after putting on 70 carbs?

  11. #11
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    have you adjusted the idle screws?
    did you rebuild the carbs?
    Aquarius Inflatable Yamaha 70 EFI
    24 Skater Twin 3.0 300x copies 113mph so far
    954-861-1611

  12. #12
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    Quote Originally Posted by berg969 View Post
    have you adjusted the idle screws?
    did you rebuild the carbs?
    I adjusted the idle speed and also tried to tune it as best as possible. I also advanced the timing slightly and it seemed to run better. Idle spped still seems a bit higher and definatly rougher running. Shakes around like a Tohatus, not smooth as silk like it was. I didn't rebuild the carbs as I know the motor they came off and it was running well on that motor. Should it be just as smooth running down low with 70 carbs? Do I need to change the jets?

  13. #13
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    have you synced them.
    Aquarius Inflatable Yamaha 70 EFI
    24 Skater Twin 3.0 300x copies 113mph so far
    954-861-1611

  14. #14
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    Quote Originally Posted by berg969 View Post
    have you synced them.
    Yep sure did.

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    sorry to be bumping this old thread! im looking to put yamaha 70 carbs on my 2006 tohatsu 50 D2, will they bolt on?

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