Sounds like a missfire

Discussion in 'Newbie Scooter Tuning' started by UGE, Apr 15, 2019.

  1. UGE

    UGE Member

    Messages:
    31
    At high revs 7k it seems to misfire and stutter a lot almost bouncing between 7 and 8k but no more acceleration and loses power. any ideas?
     
  2. milo2025

    milo2025 Trip to Trumpton

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    727
    That doesn't sounds good. Could be the valves hitting the head gasket or even worse the big end's gone. I remember this problem when engines changed from using leaded to unleaded. The lead would act as a kind of protective coating and prevented pinking and knocking due to the higher octane level.
     
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  3. UGE

    UGE Member

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    31
    It did it when it had a 50 block on and now got a mallossi 70kit on still does it but no valves to hit also turned over by hand when fitting 70kit and nothing touches.

    I am running V Power in it tho
     
  4. milo2025

    milo2025 Trip to Trumpton

    Messages:
    727
    Do you know if it uses rocker arms or camshaft? Rockers were more tolerant but less efficient. V power could be the problem! Best to run on regular. I've heard folks having problems using super high octane unleaded in scoots.
     
  5. UGE

    UGE Member

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    31
    not a clue its a 2010 runner
     
  6. milo2025

    milo2025 Trip to Trumpton

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    727
    I want a runner 180 to replace my speedfight 100. What size is your engine?
     
  7. UGE

    UGE Member

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    31
    was 50 but now 70
     
  8. milo2025

    milo2025 Trip to Trumpton

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    727
    70. just read you're previous post. sorry mate.
     
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  9. UGE

    UGE Member

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    31
    no worries, yeah the damn things giving me such a headache just want it running
     
  10. milo2025

    milo2025 Trip to Trumpton

    Messages:
    727
    I'd hang tight till someone like scuba or stevep come online and give you proper advice. I'm a bit of a novice to be honest.
     
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  11. scubabiker

    scubabiker NITROJUNKIE

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    7,321
    Running too lean...
    That lack of power is your engine getting hot
     
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  12. UGE

    UGE Member

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    31
    What would you recomend? Im currently on an 68 jet and have sports exhaust fitted as well (standard 17.5mm carb)
     
  13. scubabiker

    scubabiker NITROJUNKIE

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    7,321
    Put a bigger main jet in it. Try 80
     
  14. UGE

    UGE Member

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    31
    Ok will give that a go.
    When i have adjusted the mixture i have been putting idle to 3k then adjusting till the revs pick up (generally hit 5k) and it sounds clean with no smoke is that rite?

    Also is the screw air or fuel?
    Im guessing un screw is more flow and tighten reduces?

    As you can see i have been flying blind having been given conflicting info from people i know
     
  15. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    3k is way to high idle...
    The mixture screw I can't know without seeing the carb, which side of the needle/main jet is the screw? (side nearest reeds or side nearest airbox)
     
  16. UGE

    UGE Member

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    31
    Closest to the airbox.

    What idle should i be at to set it?
     
  17. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    It's an air screw then. Turning out lets more air in.
    Idle should be about 1.5k
     
  18. UGE

    UGE Member

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    31
    Makes sense

    Just put 80jet in so is it just a case of all the way in and 1.5 whole turns out with the screw then just tweek till it sounds smoothish?
     
  19. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    Yeah that's the ticket.
    It's wise to blip the throttle between adjustments then wait 20 seconds to see if it creeps down or up.
     
  20. UGE

    UGE Member

    Messages:
    31
    Thanks will give it a go. Just trying to get it to fire up now lol
     

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