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  1. #1

    Default Yamaha 25 HP 2-stroke

    I have a 2007 25 HP Yamaha outboard. Recently ithas not been running right at low idle (anything below the start position on the tiller). It runs fine at high idle. I troll with it alot and when it is in gear, it runs fine. When I take it out of gear, it runs and about every 5-10 seconds it has what I will describe as a hiccup or pop. Occasionally this hiccup/pop causes the engne to stall. As I said, the hiccup/pop does not occur when the engin is in gear. It also does not happen only after trolling for a while. I can run at full speed for ten minutes or more and when I idle down and take it out of gear, it starts again. Yesterday I changed the plugs, dumped out the gas that I had in it and replaced it, and added seafoam to the gas. I also checked for leaks or other problems with the fuel hose and could not find any. Does anyone have an idea what the problem might be and how it can be corrected?

  2. #2
    Join Date
    May 2011
    Location
    Alaska
    Posts
    289

    Default Re: Yamaha 25 HP 2-stroke

    This may be a simple fix. It sounds like your idle stop screw may need to be backed off a little to reduce the amount of air through the throttle plates. The other possibility is that you need to enrich the idle mixture slightly. What is happening is a lean sneeze or backfire. Changing the mixture may mess with your trolling so try backing out the stop screw a little bit. It is on the upper carb and controls both carbs via the connecting link rod. If that makes your idle speed too slow then you may need to open the mixture screws a bit. Those screws have limiters on them and may already to the limit in which case you will have to remove the limiter cap. BE CAREFUL the screw is fragile and will likely break off. One mixture screw on each carb. Stbd side angles up at about 45 degrees.

  3. #3

    Default Re: Yamaha 25 HP 2-stroke

    Thanks, I'll see if I can figure it out.

  4. #4

    Default Re: Yamaha 25 HP 2-stroke

    I'm not sure which is the idle stop screw. Can you please advise?

  5. #5
    Join Date
    May 2011
    Location
    Alaska
    Posts
    289

    Default Re: Yamaha 25 HP 2-stroke

    Look at the linkage on the side of both carbs. One of the carbs has a screw with a spring wrapped around it which the throttle linkage stops against. Vertical orientation.

  6. #6

    Default Re: Yamaha 25 HP 2-stroke

    I figured that was probably it. I think what your suggesting is to turn that screw a bit (like maybe a 1/4 turn) while the engine is running to see if that gets rid of the pop. Is that correct? Is that rod tapered? What stops the spring on that rod from completely decompressing as soon as that screw is loosened?

    Thanks for taking the time to help.

  7. #7
    Join Date
    May 2011
    Location
    Alaska
    Posts
    289

    Default Re: Yamaha 25 HP 2-stroke

    I'm not talking about backing the screw out enough to untension the spring. 1/8-1/2 turn will be enough unless your carbs aren't synched, in which case someone who is familiar with the process needs to look at it.

  8. #8

    Default Re: Yamaha 25 HP 2-stroke

    I was having the hardest time trying to figure out what you were talking about, as I could not find a screw with a tensioning spring on it anywhere. I new (or at least thought I new) what you were talking about, since I have adjusted the carbs on other small motors before, but nothing with two carbs. Then I looked more closely at the carb-synching connecting rod. Near the top-carb end of that rod there is a threaded hole with no screw in it, which allows, im thinking, the idle adjustment to go past what should be its lowest point or influences the relationship between fuel flow and carb setting or some such thing. Am I on the right track here? I looked inside the housing and could not find the screw or spring, but there is alot of area that I cant see. I'm hoping to just be able to buy the screw and spring and see if that takes care of it. I'm not sure how far in to set the screw, but I suppose I could fool around with that when I have it running in the driveway.

    Thanks alot for your help. I'm on the water about every other day with that thing at this time of year and I dont want any downtime having it at the shop. I'm hoping you may have saved me a trip to the shop.

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