Thread: Johnson "70mod"

  1. #291
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    the slip would be around 8% if its the srx and running 23 pitch. that is good for srx prop.
    it probably is 23 again because the blades are bent down not up, and you added a touch of pitch to leading edge, so 23 pitch again.

    the main thing is it it going fast, so slip dont realy matter, the boat looks good too.

    what is pull away like ? is it better with the ring you made for gearcase ?

    and will you be putting solid mounts in the bottom now you are running surface ?

  2. #292
    Team Member hupiveneilija's Avatar
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    30sec wot, boat on trailer with my testprop. Anyone?
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  3. #293
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    I Think maybe a bit lean,
    a bit hard to tell looking on pc rather than in front of me.

    would you call this light tan or mid tan ?

    for running long fast runs at very high RPM i would prefer slightly darker colour on the plug core...

    is this a clear colour 2 stroke oil ? and is it fully synthetic ?



    when you done this plug test did you switch engine off in gear at WOT or did you let it slow down before switching off ?


    hope this makes sense.

  4. #294
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    well after reading a bit about plugs and rich lean etc it seems I have been mis-lead a long time ago on how to look at the plugs.
    I always thought it was the porcelain colour to be looking at, turns out its the outer ring that shows the rich/lean !!!!!

    here is a pic explaining where to read the mixture .
    if this is correct then the plugs on your outboard are showing its way too rich ?
    the pic at top left of a plug is from a site saying this plug is too rich also . ( I thought that was fine to be honest )

    anyone else want to chime in on this as I am now a bit confused, and will be ordering a spark plug reading tool .

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  5. #295
    Team Member LittleCharger's Avatar
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    Jennings article on plug reading. Tough to read a plug properly if you can't see the area you need to for jetting. I prefer to read piston wash and use the plugs as a secondary source as well as plug temp

    https://www.strappe.com/plugs.html
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  6. #296
    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by LittleCharger View Post
    I prefer to read piston wash and use the plugs as a secondary source as well as plug temp

    https://www.strappe.com/plugs.html
    Me too. After every run i take plugs out and with flashlight i can see piston top for wash. Yesterday went out and ran 20 litres through the engine, first time ever cant see washmarks because there arent any. It was so rich that piston is as clean when
    installed but wet as hell! Might need little smaller jets

  7. #297
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    Quote Originally Posted by hupiveneilija View Post
    30sec wot, boat on trailer with my testprop. Anyone?
    So these have too much color, need hotter plugs i suppose. In champion world smaller or bigger number?
    Ive read that LC's posted GJ article, wich was good, if i understood it right look of the centerelectrodes tip is very near what it supposed to be in ign wise, correct? There is film but electrodes tip is clean and sharp if focus that last picture.
    Insulator could be lighter in color so hotter plugs?

    This most technical english is quite difficult to understand from time to time, even when read multiple times with tought.

  8. #298
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    reading piston wash is something I have never done to be honest, not realy a clue about how to be accurate or even close to check mix by this..
    I think I have it all the wrong way as I would see it as dark piston top too rich, clean piston top good clean burn ?????

    here is two different piston top pics I took with endoscope on android phone a short while back,

    would this be a lean mix or rich mix ?

    what do these 2 pics say about the way engine is burning the fuel ?


    compression is 145-147-146 cold cranking ..
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  9. #299
    Team Member hupiveneilija's Avatar
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    Clean top without carbon is too rich, mixture is so dense that it kind of rinse piston clean.
    Little black haze or little thicker for longer period of time with about littlefinger thick clean areas in front of transfer ports is good IMO.

    Flat top piston is harder to read than slight dome one. And mainport tells better than boostport.

    Those pictures imo are rich or not driven hard enough😉.

    Somebody may correct if im in the woods with this matter😂.

  10. #300
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    these pics were taken after just average ride at max of 6,000 rpm with 13x19 prop.
    and these are original pistons never been out the block since new. 1995.

    these large bore (70hp) Black top carbs were jetted originaly with the jets that are in now .. 50D at the bottom mains and 55D at the tops.

    the next carb jet change was in 1994 when omc switched to using 53D bottom main and 55D at the top.

    then in 1995 they changed the jets again and went to 52D at the bottom mains with 60D at the tops. and kept this size all the way till end of production.

    Maybe I need to find some 52 and 60 jets to give it a try, that would give a touch more fuel and a touch more air and maybe more power too ?
    finding them over here will be a nightmare !!!

    the carbs this motor originally came with were the smaller 60hp carbs with 45D at the bottom main and 35D at the tops.
    so I would imagine it was running a bit on the rich side all of its life before me..

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