Thread: Johnson "70mod"

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    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by LittleCharger View Post

    Put the big pitch on her and spin her up!
    First have to find one! Its not easy.
    Asked about 2 blades on other topic.

    Hey, its fishing motor. Not suppose to go almost 58kn😂😂.

    Btw can one hear too early ign timing or is it just little driving and take plugs out to see them.
    Sligthly tempted to try more timing.

  2. #152
    Team Member LittleCharger's Avatar
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    Quote Originally Posted by hupiveneilija View Post
    First have to find one! Its not easy.
    Asked about 2 blades on other topic.

    Hey, its fishing motor. Not suppose to go almost 58kn😂😂.

    Btw can one hear too early ign timing or is it just little driving and take plugs out to see them.
    Sligthly tempted to try more timing.
    You can hear if you know what you are listening for but most of the time people find out to late lol...some guys run 21 but they typically drag race.

    Two blade are not as efficient I'd look for a three blade.

    Good speed should be able to get another couple mph out with some bigger pitch

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    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by LittleCharger View Post
    You can hear if you know what you are listening for but most of the time people find out to late lol...some guys run 21 but they typically drag race.

    Two blade are not as efficient I'd look for a three blade.

    Good speed should be able to get another couple mph out with some bigger pitch
    Have to concentrate on 3blade, might be also better when things get rough and choppy.

    Think that smallchamber head have better control on combustion and firing, so it might be able to use more timing. Have to keep things on a rich side.

    Hah, had cold ring under *** yesterday; tought that something is happening cause engine started to slowing down repeatedly. My bad had forgotten airscrew on the tank closed, so tank was all sucked in. Open screw and off you go!😂

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    there is lots of props for sale but all too far away in the usa and the price for postage is just so expensive, plus taxes.

    can always get a srx for a v6 and get rehubbed for 13 spline. and take down to 14 inch diameter.

    if you have a press you could do this yourself, just make a ring to help guide it in with dish washing soap for lubricant.

    but again its hard to find the right sizes here in Europe.

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    Team Member hupiveneilija's Avatar
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    Quote Originally Posted by hupiveneilija View Post
    Some stuffing.
    Went testing today. These stuffings over the reeds, with white plastics on place its a little stronger under 4000rpm but on high rpms kind of fighting against itself and is not revving freely. Lost about 4kn on top speed. So leaving only that blue epoxy on its place. Might try also with Boyesen reeds, then its without stop plates and epoxy what makes primary comp even lower. Will see how it works.
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    Air temperature and pressure will slow you down today by a good amount.
    today all across Europe the temp as gone up a few degree and barometric air pressure is at a real high today and tomorrow, that will make boat slower.

    I think trying to use that blue stuff for stuffing the crankcase will fail time after time. its not going to be ethanol proof !!!!
    its not the gasoline/petrol that will break it down its the oil and the ethanol that will cause its destruction.

    you need to find out compression and revs before you do anything else, maybe your compression is above the 160 psi mark ?
    you might need to find some high octane fuel and try that next, if compression is over 160 psi that just might be a problem.

    the reeds you already have are what make ? they are not omc reeds.

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    Team Member LittleCharger's Avatar
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    Quote Originally Posted by hupiveneilija View Post
    Went testing today. These stuffings over the reeds, with white plastics on place its a little stronger under 4000rpm but on high rpms kind of fighting against itself and is not revving freely. Lost about 4kn on top speed. So leaving only that blue epoxy on its place. Might try also with Boyesen reeds, then its without stop plates and epoxy what makes primary comp even lower. Will see how it works.
    Hard to believe the stuffing is knocking that much mph off, typically increasing crankcase compression has little effect on top end.

    I don't think you will find any more mph in reed changes either.

    Air temp and pressure do impact as Phil commented but not 4 knots in our experience from the best fall days to worst summer humid days.

    Compression is the best bang for the buck I'd focus on increasing it, I think you mentioned you are 145ish ?

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    Quote Originally Posted by LittleCharger View Post
    Hard to believe the stuffing is knocking that much mph off, typically increasing crankcase compression has little effect on top end.

    I don't think you will find any more mph in reed changes either.

    Air temp and pressure do impact as Phil commented but not 4 knots in our experience from the best fall days to worst summer humid days.

    Compression is the best bang for the buck I'd focus on increasing it, I think you mentioned you are 145ish ?
    Came just from testdrive 2person and full tank 40l. 54kn with 2, 56kn with one. Took plastics away, spins more freely on top. 3kn more than yesterday. Those are driven wind behind the back. Other way 2kn lower. It was cooler week ago when I went 57,4kn, today much warmer, propably too rich.
    But yes have to take that comp higher somehow, that 0,5mm thinner gasket might help a little allthough my engine has quite worn pistons&rings. Have to take that head to machine shop and take half mm off of it.

    It sounds kind of a healthier now. Measured comp psi on warm engine between 145-150. Could use more.

    I have another block wich Ive cleaned up, have to take 0,5mm off of a deck heigth and then put smallchamber on it with 1mm gasket.

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    forget the small chamber head, get a normal head and take off 1.5mm then you will have the compression bumped up very high.
    you want top end power for the high speed, normal combustion chamber width is best for higher speed.

    and the weather is not just the hotter air, it is very high pressure these last few days, that will slow you down maybe 2-3mph compared to the
    cold low pressure weather a week ago.

    what ratio are you using for the 2 stroke oil/petrol mix ? and what 2 stroke oil you using.

  10. #160
    Team Member LittleCharger's Avatar
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    Quote Originally Posted by filthy phill View Post
    forget the small chamber head, get a normal head and take off 1.5mm then you will have the compression bumped up very high.
    you want top end power for the high speed, normal combustion chamber width is best for higher speed.

    and the weather is not just the hotter air, it is very high pressure these last few days, that will slow you down maybe 2-3mph compared to the
    cold low pressure weather a week ago.

    what ratio are you using for the 2 stroke oil/petrol mix ? and what 2 stroke oil you using.
    High pressure is actually your friend from a power point of view.

    Need to consider elevation, humidity, pressure and air temp to determine relative air density which is what you want to jet off of.

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