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  1. J

    1975 Johnson 25 hp surging

    Re: 1975 Johnson 25 hp surging Sorry, that was difficult to see. In this you can see where the two lines I drew were.
  2. J

    1975 Johnson 25 hp surging

    Re: 1975 Johnson 25 hp surging Thanks! I took the "plug" out and I replaced the failed thermostat. I also replaced the J4C plugs with J6C. It ran better than it has since I have been working on it. It ran really well at WOT for about 10 minutes and then the revving" or slipping started...
  3. J

    1975 Johnson 25 hp surging

    Re: 1975 Johnson 25 hp surging Here is the diagram. I was planning on taking it out this afternoon and running it. I would like to leave that plug out and try it, only thing that worries me is that someone figured out something particular to this motor and did that to make an adjustment to it.
  4. J

    1975 Johnson 25 hp surging

    Re: 1975 Johnson 25 hp surging Thanks for the comments. I added another picture. This "plug" looks like something that was manufactured, not a piece of melted rubber or something that was sucked up into that postion. If you look at this pic you can see a taper at the bottom and a well...
  5. J

    1975 Johnson 25 hp surging

    Re: 1975 Johnson 25 hp surging I am changing out my thermostat today. The old one was failed open. I found this rubber plug (see pic) in the hole that was just beneath it. It was not in one of the bolt holes, there are 3 of those. it does not say anything about it in the service manual and...
  6. J

    1975 Johnson 25 hp surging

    Re: 1975 Johnson 25 hp surging Thanks for the responses, no it is not a violent jerk. More like you said, it revs up and the boat slows down. But it will not re-engage until I let off the throttle. I saw a post that said you can draw marks across the prop and the end of the shaft with a...
  7. J

    1975 Johnson 25 hp surging

    Have a 1975 Johnson 25HP model 25R75B, pull start, short shaft. I was having an issue where the motor would run fine at idle and whenever I would open up the throttle it would surge. If I pumped the primer bulb it would pick back up and run fine. It would not run at WOT. I could not pump the...
  8. J

    1975 Johnson 25 hp impeller problem

    Hello, new to this site. I recently inherited a 25 HP Johnson from my grandfather. The motor had not been run in about 8 years or so. I rebuilt the carb, changed the plugs, changed the lower unit oil and changed the fuel lines. Most recently I just got through replacing the impeller. In...
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