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  1. #1
    Member
    Join Date
    Feb 2017
    Location
    Nashville
    Posts
    536

    Rough Idle Issue

    I have an 05 Optimax 115. I dont know the serial number but this is just a general question really. I live in TN and once it got pretty hot this summer in June, my engine developed a rough idle after it got hot during the day. It would start out fine in the morning, start fine, idle fine, but it seemed once it got hot during the day it would not like to idle very far. If I idled just a little bit it would be fine but it I idled 200 or 300 yards it would spit and sputter. It did this most of the summer until it got really bad. I took it into a reputable shop that a lot of people on here use. They said nothing was wrong with the engine. Put some fuel treatment in it and the first couple of times out it idled well. About 3 weeks later the rough idle came back but it wasnt really bad. Same thing. First thing it would idle fine to start but after running around if I sat it down and idled around for some time it would spit and sputter. Mainly going back to the ramp because of a no wake zone.

    Fast forward to cooler temperature and the idle has been fine. I even graphed a few ledges this past weekend for 10 or so minutes without it missing a beat. The past three times out it has been running like a top. All year I havent had a problem getting on plane and it has ran great at full throttle. It just idling where it spit and spluttered. Any ideas if hot temps were the problem now that I havent had a problem in the cooler temps? Do I need new fuel lines by next summer? was it vapor lock? Im confused but relieved that the rough idle seems to be gone. I need to be able to idle because I fish the Tennessee river almost exclusively haha

    Thanks

  2. Member
    Join Date
    Jun 2013
    Location
    LONGVIEW TEXAS
    Posts
    13,941
    #2
    possibly , if they are older I would change them out for sure, poor fuel boiling due to high temps some fuels have very low boiling or vaporizing point, good luck
    .................................................. ...the scariest thing in life is the unknown ...................................

  3. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #3
    Agreed- fuel or fuel grade are a possibility, as are fuel lines/bulb. Make sure to pump the bulb firm before every start (especially in warmer temps), and keep up with the Recommended Annual Maintenance.

    Moving thread to the next forum up (smaller displacement 2-stroke models).


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