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  1. #1

    Join Date
    Jul 2008

    1999 Yamaha XL760 Low RPM Miss

    I have a 1999 Yamaha XL760 that runs pretty well. However, during low rpm cruising, it has an occasional miss. It goes away under hard throttle and it starts fine, but if I want to simply cruise around the river, it has this annoying miss. Its been doing it for a while, as I chalked it up to being normal for a two stroke engine.. Is this normal? If not, where do I look first? I have replaced the plugs with no noticeable difference. Should I rebuild the carbs?

    I have been using Ultramar TCW3 snowmobile oil,could this be causing issues?

  2. #2
    Generally this is normal because of typical non-efficient scavaging of a two-stroke at low rpm's. I believe it's aggrevated when you don't have PV's to help with pressure wave stxr has no PV's and always misses at low R's, but I purposely run that a little rich. It will be worse for you in the summer with heat and humitity. I think you may need to consider a carb re-build though if you're gonna keep the ski. The Mikuni manual says you'll tend to run rich down low when the pop-off spring get's too soft and worn...that's if you have an excel pump on that ski. How long have you had the ski/was it always doing that? Also, are you running too cold of a plug?

    BTW, I suggest you change your injector oil. Snowmobile oil, if air cooled, uses API specs for formulation and tends to be thicker kinda like the Yamalube stuff for stock ski's with catcon's.... .

  3. #3

    Join Date
    Jul 2008
    So how hard is it to rebuild the Mikuni carbs?

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