Thread: Johnson "70mod"

  1. #61
    Team Member zul8tr's Avatar
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    Quote Originally Posted by filthy phill View Post
    Zul8tr
    you said
    "Higher exhaust porting yields less static compression pressure because less cylinder volume from TDC to top of port. Most stock 2 cycle outboards are about 6.5 compression ratio (CR) relative to top of exhaust port, if you raise the exhaust ports that lowers the CR relative to exhaust. "

    to counteract the raising of the exhaust port (40 thou) many things have been modified.
    The idle reliefs have been closed off ? this should raise compression.
    the head being skimmed ? this should raise compression.
    and the combustion chamber itself being reduced to about 2/3rds its normal size ? should dramatically raise compression on its own..
    these 3 factors should of raised the compression to far exceed that of the OMC SST60.

    I think another known to be reliable compression gauge would be a good idea to know what is realy going on, simply because 145 psi is not
    even close to what is considered a high compression OMC 56.

    I would of been expecting atleast 175 psi, then bed in and make around 180 to 190 psi .
    In my statement I was referring to a relative change in pressure with previously all else remaining the same. You are correct other things were changed so why the low psi? What was the compression pressure before all mods?

    Not being familiar with your engine internals not sure how idle reliefs would affect compression psi.
    Yes on head work to increase compression psi.

    Redo the compression test with the cylinders oiled up to better seal the rings. If great difference the rings leak a lot, if not it is what it is by that gage.

    Do a leak down test.

    Yes possibly a different compression gage would give higher psi? Regardless because different gages will read different. I only use Bourdon mechanism type gages for relative differences in psi rather than absolute pressure psi and I always use the same gage to preserve the accuracy of relative psi measurement differences. Bourdon type gages are simple diaphragm expanding mechanisms that are calibrated to a standard using a dead weight tester or other accurate reference testers. Unless calibrated you will find differences among gages since you will not know the past history of the gage treatment and even new identical gages will read different.
    " Three may keep a secret if two of them are dead" Ben Franklin

    Location: SW Orlando, Fl

  2. #62
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    I just looked at the picture of the spark plugs, why the thick copper washers ?

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    did you balance your testing prop ?
    I had a prop that was terrible for vibration, once I balanced it there was no more problem.

    but I also have a prop that when balanced is still crazy for vibration..

  4. #64
    Team Member hupiveneilija's Avatar
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    https://youtu.be/XZ6xrDQQnxw
    Is this fourstrouking? Seems like there is pretty much unburnt mixture coming from exhaust. So something has changed😂. Hesitates in lower rpms like i think cause by overrich mixture. And then there is that stock tuner wich propably makes it feel kind of "liveless" on high rpms. That vibration i mensioned with "testprop" , its the engine itself.
    Ignplugs threads are that much shorter now on the head.

    https://youtu.be/mYgMwxCKJE8
    Too much primarycomp might cause that unburnt mix going through engine?
    HAH, my tach dont show over 7k, needle dont know what to do!😂
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  5. #65
    Team Member hupiveneilija's Avatar
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    Took away stuffing i made around reeds, dont push mix to the exhaust on idle anymore. Those plugs i made for comp relief holes, same stuff as nosecone, are gone. Infact i think they were gone by the time i made comp test. Maybe thread and little setscrew. Went out today, ran 45.5kn with 18 raker, dont know revs cause needle stops little over 7k. Have some water issue, dont idle good on water or flushhose. Without better, might be headgasket. Is there a chance that headgasket blows with too much waterpressure? Little lazy for going on plane under 3k especially with raker, dont slip enough, but when nose go down then it goes. Feel like needs to start playing with tuner. But before that i try with srx how it works.

    Sorry for tight typing😊
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  6. #66
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    No it is not too much compression.

    you are not firing on all 3 cylinders all the time. there is no crisp 2 stroke sound.
    before on your older video showing boat going fast your engine sounded very crisp , very good.

    what oil and fuel are you using now .
    what are the plugs ? Champion QL77JC4 ? or Champion QL78YC .

    you will always get some 2 stroke oil in the water from the exhaust, that is normal.

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    with 18 raker it should fly from zero. 18 is small for that motor . maybe need 12 to 13 mm vent holes, omc vents are too small.

    have you tried with plugs and no copper washer ? it will let the spark be in the correct place to fire.

    I also asked lots of people about the tuner to make it shorter, but everyone who is expert on tuners say you will lose bottom end power on v hull.
    short tuner just for very light tunnel hulls. ?

  8. #68
    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by filthy phill View Post
    No it is not too much compression.

    you are not firing on all 3 cylinders all the time. there is no crisp 2 stroke sound.
    before on your older video showing boat going fast your engine sounded very crisp , very good.

    what oil and fuel are you using now .
    what are the plugs ? Champion QL77JC4 ? or Champion QL78YC .

    you will always get some 2 stroke oil in the water from the exhaust, that is normal.
    It might run little better with QL78YC, tried both. Yes i know there is always oil in exgases but it was like pouring through before took stuffing out. It may have weakened lower end a little bit.

    Think that transfer timing is too much, causing that lame lower rpm behavior

    I run our 98e5 with some fully synthetic oil ment for bikes.

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    have you tried with extra spark plug washers taken off ?

  10. #70
    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by hupiveneilija View Post
    Those plugs i made for comp relief holes, same stuff as nosecone, are gone. Have some water issue, dont idle good on water or flushhose. Without better, might be headgasket. Is there a chance that headgasket blows with too much waterpressure?
    Ordered J-B Weld HighHeat epoxy putty for relief holes and solved the water issue; What a dumbass I am, forgot to retighten the head bolts so they werent tight enough and water went to cylinder(s) and gasket was also broken between thermostat and #1.

    I bet it run better after fixing those.

    Good night everybody!

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