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  1. #1

    Default miss/sputter/hesitation at idle but runs fine at higher rpm's

    i have a 1978 Johnson 85hp motor that has a slight hickup/misfire while at idle speed, but I can throttle up and while driving it will never show itself, but once it's back down to the low rpms of idling it has a hickup where it's a momentary non fire or mis-fire. Caused it to stall once on me today. Any ideas on what it could be?
    I was thinking maybe the magneto is getting weak?

    I just put new spark plugs in it thinking that was the problem but it wasn't.

  2. #2
    Chief Petty Officer kmarine's Avatar
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    Default Re: miss/sputter/hesitation at idle but runs fine at higher rpm's

    are your spark plugs clean? 2 stroke motors are notorious for fowling plugs at idle. Also what is your idel rpm. If it is too low it may tend to sputter. Otherwise you may have to look into carburaator cleaning to make sure your idle jets are free of varnish deposits.
    Kmarine Restoration services
    1995 wellcraft martinique
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    Default Re: miss/sputter/hesitation at idle but runs fine at higher rpm's

    kmarine has provided an appropriate comment. It's common to have a "lean sneeze." An occasional miss at idle. That's a carb problem. When the engine idles, the carb butterflys are closed. The idle air is provided through the holes in the butterflys. Special dedicated idle passages cast in the upper carb body provide fuel through them-they are very small. Over years of time, they can reduce in size due to dried fuel. When these passages restrict-it will run lean and miss every few rpm's. Once you crack the throttle, even a little-other jets will provide fuel and the engine may seem to run normally. You'll need to tear the carbs down and clean out those idle passages with a carb cleaner, like the aerosol cleaner called Gumout.

  4. #4

    Default Re: miss/sputter/hesitation at idle but runs fine at higher rpm's

    well i just rebuilt the carbs and installed new plugs at the same time. I thought i did a good job on the carbs since I'm usually pretty good at that, but I guess I could pull them off again and re check everything. I let the bodies soak in carb cleaner for over 12 hours when i did the rebuild so I assumed they were alight.
    I've since run it about a total of 15 min since the carb rebuild and new plugs, which was yesterday. It had the "miss" before the rebuild as well, but it wouldn't idle to well and stalled when i tried to put it into gear.

  5. #5
    Chief Petty Officer kmarine's Avatar
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    Default Re: miss/sputter/hesitation at idle but runs fine at higher rpm's

    Just curious on the quality of your fuel. Are you using fresh gas and filters ? Do you think you are running rich or lean? How many rpm is your boat idling at. Is your engine running at temperature or is it running cold or hot. There are many other things to consider when tuning, however I think you are on the right track. Make sure that your carbs are clean. I have had to rebuild carbs a couple of times and mess with float levels at times before they run perfect. Tuning is only effective if all the jets and seals are working properly. persistance is sometimes the most frustrating part of tuning 2 stroke engines.
    Kmarine Restoration services
    1995 wellcraft martinique
    mbsports boss 210
    1998sea doo gtx

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    Default Re: miss/sputter/hesitation at idle but runs fine at higher rpm's

    You may want to spray the aerosol cleaner through one passage on one carb, noting the spray pattern exiting the carb. Then do that same passage on carb #2, again noting the spray pattern exiting the same orfice-comparing it with that of carb #1. Then go on to the second passage on carb #1, and repeat this process on all. You want to have the same spray pattern exiting similar passagesways on both carbs. If one is restricted, you will see it with this method.

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