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Thread: yamaha 70 ces

  1. #11
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    i have sat about 3ft away from that style, turnin it into the 8's. only lightened the ring gear. it's when you clean off the alu, on like an OMC wheel, it weakens the hub, lowers the integrity of the G' force thresh hold, or the point at which they come apart.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  2. #12
    Team Member Roflhat's Avatar
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    Does the lightened flywheel make a big difference on the CES? I'm going pull start only so I could remove the ring gear completely

  3. #13
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    just lets it spin up a small small small bit faster, makes it jittery at low speed. ive never ran a 70 hub only, have ran a 50hp hub only, there is some clout to the idea that the ring gear reinforces the hub on that style. ? about 60hp tunnin 7's just the hub was good. more power and turnnin faster i can't say if it would stand up.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  4. #14
    Team Member Roflhat's Avatar
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    Ok, I'll probably leave the flywheel for now. What gains are there with the 90 carbs? I've got a set of round bowls which I can put on but I don't want to lose any bottom end

  5. #15
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    90 carbs need a welded crank, round bowls need a hole in the tray to fit, air box, choke plates, reed stops go in the trash. the intake needs to be opened to the size of the 90 carb base gasket, 8-9hp gain, pull the 165 mains out of the 90carbs pull the 160's in out of the 70hp carbs put them in the 90 carbs. you won't notice any low end loss, make new throttle cam.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  6. #16
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    there is a shim plate on the intake, it needs it or the crank will hit the reed blocks and she will lean out and Boom,

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  7. #17
    Team Member Roflhat's Avatar
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    Thanks Fred,
    Sounds like a decent gain from the carbs. I had a look at them and it looks like the mounting bolts are different patterns? It doesn't have an air box, I'm getting some velocity stacks for it. The reed stops are still on but I'll remove them when I put in the CCM reeds. Not sure about the choke plates, I quite like having chokes. Do you swap the throttle roller on the 90 carbs? Mine have it on the middle carb whereas the 70 is on the bottom carb. Do you just swap the carbs and chokes about?

    Thanks for the tips on jetting and the shim, saves a lot of hassle! Have you got any photos of your throttle cam?
    I'm getting a billet head for it with positive squish, think I'll leave the ports alone for now. The crank will be getting welded at the same time

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    Quote Originally Posted by Roflhat View Post
    Thanks Fred,
    Sounds like a decent gain from the carbs. I had a look at them and it looks like the mounting bolts are different patterns? It doesn't have an air box, I'm getting some velocity stacks for it. The reed stops are still on but I'll remove them when I put in the CCM reeds. Not sure about the choke plates, I quite like having chokes. Do you swap the throttle roller on the 90 carbs? Mine have it on the middle carb whereas the 70 is on the bottom carb. Do you just swap the carbs and chokes about?

    Thanks for the tips on jetting and the shim, saves a lot of hassle! Have you got any photos of your throttle cam?
    I'm getting a billet head for it with positive squish, think I'll leave the ports alone for now. The crank will be getting welded at the same time
    All of the throttle shafts should interchange. I just went through this with my little Yamaha.

  9. #19
    Team Member Roflhat's Avatar
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    Quote Originally Posted by Tiller guy View Post
    All of the throttle shafts should interchange. I just went through this with my little Yamaha.
    Excellent thanks

  10. #20
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    just a 70hp gasket set, on the rings, the stock ces pistons run a thin ring high up close to the crown, never could order them rings. on the ces head, with a nose cone on a tunnel inflatable it will push the water plugs out of the head, i would take the extra washer off the head bolts, make a cover plate for the head (same thickness as the washers), that keeps the plugs in.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

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