Thread: Fast Fred's OMC Mod 50 secrets Thread #2

  1. #741
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    well not sure what your lookin for, but see if we can work it out. Standard aka short shaft, gots a Nitro foot with new bearins and seals and the big shift dog. this is were i'll start

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

  2. #742
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    Question?(s) Short shaft reeds/blocks different than 20" reed blocks on a 49 triple? If the intake side of the 49 is in " a high state of tune", and then some Gumba swaps powerheads, can this be anything to cause performance probs? I got a 78 powerhead on a 1975 -70hp. looks like same Part#. She don't snort outta the hole like my 65 Evinrude triumph did. goes like hell once its up n out though. fishin moda. seein a little spitback on #2-#3 carbs when you begin to open throttle. #2-#3 plugs seem to run wet. #1 is dry, tan.
    1975-76-78 they ran one part# for 75hp short or long mid.
    0382442 LEAF PLATE ASSEMBLY. 70 HP MODELS ONLY.
    0386798 LEAF PLATE ASSEMBLY. 75 HP MODELS ONLY
    1979 they got all specific
    0389553 LEAF PLATE ASSEMBLY. 70 MODELS ONLY
    0386798 LEAF PLATE ASSEMBLY,15" transom. 75 MODELS ONLY
    0389731 LEAF PLATE ASSEMBLY,20" transom. 75 MODELS ONLY

  3. #743
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    Soon I'm going to try 85 Yamaha motor boats of science that I for the first time I try Yamaha engine because I love engines Jawnson much

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    Can anybody school me on exhaust tuners? How the length and the opening size effects the performance. I'm building a long shaft 56", 70 hp., tiller, so far I clean up the intake passages, opened up the reed stops a hair, beveled the exhaust ports, put three new slugs 0.020" over and shaved the head 0.055" over. The power head is back together and I started thinking about the tuner, should I leave it alone or tinker with it?
    Mike

  5. #745
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    the exhaust determines where your peak power is and how wide a band that is.
    Not so easy on a outboard as no gears and you have to get onto the plane
    Its the science of sonic waves

  6. #746
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    Default h.p in a can....:)

    Split a can of Seafoam between two 6 gallon tanks. one tank had 4 gal. in it the other was pretty full. She fouled the plugs....just like people warn about....which is what I hoped for... but the hesitation and spit back are gone.....I threw in the new set of plugs....runs nice now.

    "If it ain't broke fix it until it is"

  7. #747
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    Quote Originally Posted by Powerabout View Post
    the exhaust determines where your peak power is and how wide a band that is.
    Not so easy on a outboard as no gears and you have to get onto the plane
    Its the science of sonic waves
    In that case maybe I should leave it alone but that's hard to do. lol
    Thanks Powerabout

  8. #748
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    Stinger tuna is about 1 1/2" long, in a 15" mid, have seen a 20" 75hp with a long tuna. SST60 style seems about best, or 6-7" long, the exit 2 1/2 times the size of the inlet. or...............

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

  9. #749
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    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  10. #750
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    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

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