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Thread: Tohatsu M50D2

  1. #1
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    Default Tohatsu M50D2

    Hi All,

    Are there any reed blocks that can be swapped into my Tohatsu M50D2? I have a modified the ports, re-angled the squish on the stock head, 70 yamaha carbs, M50D1 tuner. My calculations show that the reed area on the stock cages are potentially a limiting factor on this modified motor. I there any reed block options for this motor? My experience with grinding on rubber coated reed cages (like the stock ones) is not good and can lead to reed failures or rubber not letting the reeds close. I can fabricate some cages but would prefer not to if there are other options.

    Any ideas?

    Thanks,

    Mark
    612-747-9701
    ehsassociates@comcast.net

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  2. #2
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    Are you related to the Fast Cats effort out of Australia?

  3. #3
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    No I am not. Fastcatt is a play on my last name which is pronounced "cheetah". Just a MN guy working on a fishing boat motor...

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    Must be possible to fit some V force reeds in there? I know the tohatsu the reed blocks are very small, V force style would give you more area if you can fit them in

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    I have been doing some research to try see what I can find but nothing so far that looks like even close to a direct fit. Some of the yamaha RD350/400/Banshee reeds look promising but they do not have the downward angles that the stock reed cages do.

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    Don't have anything to add. Are those ports in your cylinder factory?

  7. #7
    Team Member Roflhat's Avatar
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    definitely a couple of finger ports in there

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    I added a couple boost ports, fixed the transfers where they enter the bore and the case where the transfers are fed. The piston wash on this motor (and other Tohatsu triples i've seen) always seemed unbalanced for a motor that had symmetrical transfers. It definitely had more wash on the lower transfers. I did some work with the intake port and the case where the transfers feed from and the wash is considerably more even. This what it used to look like.

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  9. #9
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    Nice! Wasn't sure if finger ports were factory in those motors. I'm used to mercs with lousy factory ports.

    So you're using the clean spots to infer chamber flow?

  10. #10
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    Hi
    Piston wash indicates the richness/leaness of a motor. The more wash (or clear spot on the piston crown) the more rich condition=more fuel. If the pumping action and/or the imbalance of fuel to air in the crankcase is significant, one side of the cylinder might get more fuel than the other (which is the case with the tohatsu triples) especially when the transfer ports are symmetrical (matched). if fuel transfer in a 2 cycle motor is uneven you are not getting all the HP that your transfer port mean area can deliver. It can also lead to uneven piston temperatures. Either way it is not a good situation for max power. My old motor as pictured above is rich on one side of the cylinder and lean on the other. All 3 cylinders were the same. After some work on bottom of the transfers and the intake it is more balanced. Attached is a picture of a motor that is running well (rich/lean) and more balanced.

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