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Thread: yamaha 70 ces

  1. #51
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    If your turning 6400 rpm with a 22 pitch. You will only gain 300 to 400 rpm dropping down to a 20 pitch. With a 1:71 gearcase You are far away from the normal 75 mph to 80 mph speed the F4 fellows run and no where near the 100 mph record. Maybe your boat is heavy.

  2. #52
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    but acceleration will be better, enhough i hope...
    Boat is light, didn't wheight it but can lift the back alone.
    Also have to watch my step while boarding or my foot makes a hole in the deck.
    It will be my driving probably, only used to v-bottoms...
    Also i'ts difficult to watch rpm, the gauge sits between my legs just in front of the seat.
    So when i'm givin WOT and trimmed out, I'm not keen to look down...
    You can feel good when you are trimmed to make it fly, boat picks up some rpm's and accelerates once more...
    Then you need to keep it like that
    Still learning to drive this boat and get the feel for it, so it will become better, faster in the future. (i hope)

    Exact speed i don't know,
    When i was driving, they where training for waterski. One boat, 21foot with 300xs i tryed to follow once.
    I could follow him, the distance between us stayed the same.
    Don't know of he was giving it all...

  3. #53
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    per yamaha top 700 \ 40 hp

  4. #54
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  5. #55
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  6. #56
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  7. #57
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    fede these attachments dont work I am very interested in 90 yamaha mods

  8. #58
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    I happen to be reading this since all I could find was a 97 yamaha 75 and I could sure use some help bringing a bit more power out of this powerhead . I understand it has same block and such as the 85 and 90 so please forward what you need to do to make this 75 improve its baseline to the 90 specs . Thanks -

  9. #59
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    Quote Originally Posted by kellytheaker View Post
    I happen to be reading this since all I could find was a 97 yamaha 75 and I could sure use some help bringing a bit more power out of this powerhead . I understand it has same block and such as the 85 and 90 so please forward what you need to do to make this 75 improve its baseline to the 90 specs . Thanks -
    I cut and pasted the below info form somewhere on the internet, but it seems plausible. If you want to be sure, trawl through one of the online parts websites like megazip or boats.net or see what parts numbers change per year.
    The carbs are exactly the same, it’s a common myth that the 90 has different carbs from the 75hp. The jetting is different but the venturi are the same. The physical differences are the 75hp had a low compression cylinder head and restricted exhaust tuner. 80hp had high compression head, restricted exhaust. 85hp low compression head, unrestricted exhaust. 90hp high compression head, unrestricted exhaust. The later 75hp may have had the high compression head fitted

  10. #60
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    Default Yamaha 75 - 90

    I appreciate the reply - still working on figuring this out . The carbs - square vs Round bowl is another question but possibly the square bowl are just on the premix motors like the 85 and such .
    Another issue I have heard is when removing powerhead to do the exhaust tuner - the bolts are usually snap off . Hopefully when I do the changes to the tuner I can get them out reasonably with heat .
    Quote Originally Posted by coleindustries View Post
    I cut and pasted the below info form somewhere on the internet, but it seems plausible. If you want to be sure, trawl through one of the online parts websites like megazip or boats.net or see what parts numbers change per year.
    The carbs are exactly the same, itís a common myth that the 90 has different carbs from the 75hp. The jetting is different but the venturi are the same. The physical differences are the 75hp had a low compression cylinder head and restricted exhaust tuner. 80hp had high compression head, restricted exhaust. 85hp low compression head, unrestricted exhaust. 90hp high compression head, unrestricted exhaust. The later 75hp may have had the high compression head fitted

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