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  1. #1

    Lets talk compression, fuel mix ratios and responsiveness...

    You'll have to forgive me, I'm not the most knowledgeable two stroke guy out there, transmissions are my specialty. So here's my story:

    Boat:
    97 Exciter
    Twin 1100 63M motors
    3 x 38mm Mikuni's each
    110-115 compression across the board on both motors

    Current mods:
    Nothing special, I put in primers, removed the choke plates, overhauled the carbs & just try to maintain it best as possible. I typically run the boat premix at 50:1 with 90 octane. I did make one mistake & changed to aftermarket reeds in the port motor (so if anyone has a set of factory reeds they want to sell cheap let me know)

    Short Term Plan:
    To change up to 12/18 & 13/19 props & pick up a little more bottom end & maybe a 1-2 MPH top end.

    Longer Term Plan:
    Rebuild both motors using brand new Hot Rods Cranks & Wiseco Pistons & OEM seals.

    What I am curious about is how many .001"'s of an inch are required to be milled from the head to get the motors in the 130-140psi range? And what the optimal oil/fuel ratio might be?

    I'd like to keep it relatively close to stock for reliability sakes but am hoping to break the 60mph barrier while still using the 38mm carbs. Current best is 57.2 on the GPS on pure glass.


  2. #2
    jdog800's Avatar
    Join Date
    Feb 2007
    Location
    Alexandria L.A.
    Posts
    812
    Quote Originally Posted by TheWanderer View Post
    You'll have to forgive me, I'm not the most knowledgeable two stroke guy out there, transmissions are my specialty. So here's my story:

    Boat:
    97 Exciter
    Twin 1100 63M motors
    3 x 38mm Mikuni's each
    110-115 compression across the board on both motors

    Current mods:
    Nothing special, I put in primers, removed the choke plates, overhauled the carbs & just try to maintain it best as possible. I typically run the boat premix at 50:1 with 90 octane. I did make one mistake & changed to aftermarket reeds in the port motor (so if anyone has a set of factory reeds they want to sell cheap let me know)

    Short Term Plan:
    To change up to 12/18 & 13/19 props & pick up a little more bottom end & maybe a 1-2 MPH top end.

    Longer Term Plan:
    Rebuild both motors using brand new Hot Rods Cranks & Wiseco Pistons & OEM seals.

    What I am curious about is how many .001"'s of an inch are required to be milled from the head to get the motors in the 130-140psi range? And what the optimal oil/fuel ratio might be?

    I'd like to keep it relatively close to stock for reliability sakes but am hoping to break the 60mph barrier while still using the 38mm carbs. Current best is 57.2 on the GPS on pure glass.
    .010 = 10psi roughly. 160psi is max pump gas safe compression.
    To get to 60 you will have to convert the 63m motors to 65u motors.(topend swap) There is a ton of information about both of these motors in the old school section.
    The boat will actually run faster with 2 people in the boat rather than one.

  3. #3
    Good point, Mods can you move this to the old school section?

  4. #4
    OK, so back to the discussion...

    .001" = 10psi?

    I find that hard to believe, perhaps .010" = 10psi?

    If I shaved .010" That'd be 100psi!!

  5. #5
    pilo704's Avatar
    Join Date
    Jul 2008
    Location
    dirty jerzz
    Posts
    830
    i got a set of oem reeds, they are like new..make me an offer

  6. #6
    Old Ski Insanity w/rpm500's Avatar
    Join Date
    Aug 2005
    Location
    Crystal River Fl
    Posts
    2,208
    .010 for 10 .. do remember its not just a flat mill cut... the domes will have to be checked for proper 'squish'

  7. #7
    jdog800's Avatar
    Join Date
    Feb 2007
    Location
    Alexandria L.A.
    Posts
    812
    Quote Originally Posted by w/rpm500 View Post
    .010 for 10 .. do remember its not just a flat mill cut... the domes will have to be checked for proper 'squish'

    im sorry ...thats what i ment just reread that

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