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  1. #1
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    Default 1957 johnson sea horse 7.5 rpms

    starts good, but when i throlle it up it rev's up half way and then when i go farther with the throttle it slows the rpms and i back the throttle back to half way it rev's back up, could it be the butterfly is in the wrong position, if so how do i adjust it, i just put new points, condensor & plugs, thanks

  2. #2
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    Default Re: 1957 johnson sea horse 7.5 rpms

    could be that when the carb starts to open, it then gets to much air because the carb jets are stopped up. or it could just need a "sync and link" to set the timing with the carb. if it just started I would look into the carb being in need of cleaning. does it hold good pressure in the tank?

  3. #3
    Admiral Chinewalker's Avatar
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    Default Re: 1957 johnson sea horse 7.5 rpms

    My guess is that you're actually only running on one cylinder... Have you checked the ignition? Try pulling one of the plug wires while the motor is running to determine whether it's firing or not...- Scott
    Share A Project Page for 1971 GW Invader Banchie 13
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    Share A Project Page for 1974 American 15
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  4. #4
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    Default Re: 1957 johnson sea horse 7.5 rpms

    how do you set "sync and link" to set the timing with the carb.also pulled a plug wire off and no change the way the motor ran (top plug) but it is getting fire to the plugs ( both of them)so be may a head gasket ? the gas tank has good pressurehelp, thanks

  5. #5
    Admiral CATransplant's Avatar
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    Default Re: 1957 johnson sea horse 7.5 rpms

    Do a compression check on that top cylinder and you'll find out if your head gasket is blown.

    Sure...go ahead and laugh at my old aluminum boat. It's paid for!

  6. #6
    Admiral Chinewalker's Avatar
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    Default Re: 1957 johnson sea horse 7.5 rpms

    Also, it's possible to have spark in the open air, but under compression lose it. Water on the plug electrode would also indicate a blown head gasket... (assuming your motor is pumping.) In any case, we've definitely determined that your motor is only running on one cylinder. Have you taken a look at the ignition components?A link and sync means adjusting the throttle cam so that the cam first hits the roller at the line in the cam. It would require loosening up one of the bolts that holds the cam to the underside of the armature plate. One of the cam's base holes is oblonged to allow adjustment. The link & sync is not your motor's running issue, though..- Scott
    Share A Project Page for 1971 GW Invader Banchie 13
    http://www.shareaproject.com/pages/p...,p,433,00.html
    Share A Project Page for 1976 American 18
    http://www.shareaproject.com/pages/p...,p,404,00.html
    Share A Project Page for 1974 American 15
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  7. #7
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    Default Re: 1957 johnson sea horse 7.5 rpms

    i did a compression test on the two cylinders and the top cylinder has about 15 psi, the bottom has about 30 psi, the head gasket is very old, but i don't see any leaks around it, when i took the bolts loose to take the head off they were not very tight, i but my hand over the cylinder and pulled the rope and it didn't seem to have very much compression, but when the piston was going back the suction was tight, any thoughts

  8. #8
    Admiral Chinewalker's Avatar
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    Default Re: 1957 johnson sea horse 7.5 rpms

    15 and 30 is WAY low. That motor isn't likely to run at all at below 60psi. BUT, it's possible that you've got a bum gauge. Borrow another if possible. Bottom line is that you want both cylinders to be relatively equal (within 5-10%). If your gauge is accurate to itself it's showing a 50% difference between cylinders - not good....- Scott
    Share A Project Page for 1971 GW Invader Banchie 13
    http://www.shareaproject.com/pages/p...,p,433,00.html
    Share A Project Page for 1976 American 18
    http://www.shareaproject.com/pages/p...,p,404,00.html
    Share A Project Page for 1974 American 15
    http://www.shareaproject.com/pages/p...,p,405,00.html

  9. #9
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    Default Re: 1957 johnson sea horse 7.5 rpms

    it will run on one cylinder(either one the cylinder top and bottom) when i take the top plug wire off can't tell much difference, but when i take the bottom plug wire off you can tell big differnce, but it keeps running

  10. #10
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    Default Re: 1957 johnson sea horse 7.5 rpms

    when the throttle is open all the way should the butterfly in the carburator be closedhow do you adjust the butterfly in the carburator, thnaks

  11. #11
    Admiral
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    Default Re: 1957 johnson sea horse 7.5 rpms

    No, it should be open like a normal motor.It sounds like something is upset on the throttle linkage. The cam on the armature plate (the plate up underneath the flywheel that turns when you advance the throttle) should push on a little lever that activates the carb's throttle butterfly. It is adjusted by loosening the bolts that hold the cam to the armature plate with a crescent wrench and adjusting the cam in and out. It should be adjusted so the butterfly *just* begins to open when the cam follower (the part that runs along the cam and opens the butterfly) is on the mark on the cam.I found this ebay image that might point out if something is missing:Click here. Did you pull the starter cord a few times with the compression tester or only once?

  12. #12
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    Default Re: 1957 johnson sea horse 7.5 rpms

    right now when the throttle is at idle the butterfly is open and when the throttle is all the way open the butterfly is closed, will their be enough adjustment to fix this or you think some thing is on wrong ?yes i pulled the rope several times, i think the compression tester is bad, also what are the instructions to remove and replace the impeller, thanks

  13. #13
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    Default Re: 1957 johnson sea horse 7.5 rpms

    sounds to me like it has been assembled wrong. maybe someone has a picture they could post, or the library may have a manual.

  14. #14
    Captain fireman57's Avatar
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    Default Re: 1957 johnson sea horse 7.5 rpms

    juke you told us that you have no spark on your bottom cylinder. Check your points/condenser and coils.
    If I wanted your advice my wife would have told me to ask you for it.

  15. #15
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    Default Re: 1957 johnson sea horse 7.5 rpms

    it is getting fire on both plugs, i took the carb. off and cleaned everything and the glass bowl and checked the filter, put new fuel lines on also, i took a little screw driver and put it in the carb. to hold the butterfly open when i rev. the motor up and it did run better, but it still vibrates more than it should, going to set the timing with the throttle and fix the butterfly so it will be open at full throttle, tell me how to replace the impeller, thanks

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