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  1. #1

    2004 Sportster 155 Engine Surge

    My Sportster engine surges between 3500 and 4500 rpm. Up and down 300 -500 rpm.
    Hot or cold engine. New plugs, fresh 91-93 octane fuel. Fuel conditioner added.
    Runs great outside of this rpm range.
    Any ideas?
    Thx


  2. #2
    buddydoo's Avatar
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    My 155 speedster did that because of Ethanol fuel,are you using non ethanol fuel?

  3. #3
    Use 93 octane fuel. I suspect it is ethanol blend, (QT). My engine is a 4 stroke.
    Your speedster is a 2 stroke, right?
    My symptoms sound exactly like the 2 stroke RAVE valve surge problem,
    but I got no RAVE valves to clean...

  4. #4
    Pwgsx's Avatar
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    Check your TPS and ICV. My boat did that and it was the TPS. Also check your throttle cable adjustment, make sure its not too tight at idle.

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