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loss of acceleration at 7000 rpms

Discussion in 'Maintenance and Servicing' at netrider.net.au started by acez1659, Sep 8, 2012.

  1. i have a 2010 250r megelli and when i get to around 7000 rpms my bike starts to vibrate heavily and pretty much doesnt accelerate past the current speed. on 4th gear i get to about 70-80km/h at 7000 rpms and even with the throttle completely open it wont accelerate any further and just vibrates even louder.


     
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  2. Given it's
    a) A single cylinder
    b) Hitting peak torque at 7,000 rpm
    c) A cheap Chinese bike
    What you're describing sounds completely normal. What were you expecting it to do?
     
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    • Like Like x 1
  3. i know people think low of a megelli as its a low quality bike but ive ridden a mates one and it runs fine and can easily get past 7k rpms without any problems.
     
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  4. In that case it would suggest that your bike is either struggling for air (check the filter), or has issues with not getting enough fuel (and if it's EFI I've NFI where to start with that).

    Other thing I'd check is the condition/colour of the spark plugs, and to make sure you're putting the right fuel in it (ie none of that 98 octane stuff).
     
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  5. Sorry forgot to mention I just got it back from a major service last week new spark plugs.. Etc. However the problems been happening since I've gotten the bike and I only use unleaded 91.
    After the service my mechanic said he'd need to rejet and give the bike some dyno time. I was just looking for a second opinion before I spend my money on a rejet and dyno time as I've also been told it might be a problem with the tube that connects to the carby or a washer which deforms under high rpms which may need to be changed?
     
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  6. You shouldn't need to rejet or dyno a bike as part of a normal service. That's usually only needed if you've made modifications to the air intake and/or replaced the stock muffler (and if either of those have been done then that's the most likely cause of your problem).

    A leak in the rubber connecting the airbox to the carbs is a possibility, usual way to check for this is to spray some sort of flammable aerosol around the area when the engine is running, and listen to see if it revs louder (start ya bastard works best, but even just cheap water dispersent will do).
     
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  7. Yeh ive sprayed carby cleaner and everything seemed normal. But I was thinking more about the tube that connects to the airbox that might be collapsing under high rpms?
     
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  8. You mean the crankcase breather, or the drain hose?
     
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  9. I had a similar problem with my GPX a year or two ago. Turned out the air intake was being blocked by a small plastic bag I had to keep a few first aid supplies under the seat.
     
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  10. too hard
    got any easy questions
     
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  11. How did you fix the problem?
     
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  12. Sorry I'm not the best at bikes as im new but it's the tube that connects the carby to the airbox.
     
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  13. I would imagine that removing the bag from under the seat would go a long way towards solving the issue :)
     
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  14. Oh lol read that wrong thought he said it was in the pipe
     
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  15. It was in the space under the seat, near the battery, toolkit, etc. From memory I solved the problem by moving it to the back of the limited under-seat space, away from the air intake. It was eventually replaced by an actual first-aid kit, which I recommend every rider carry with them.
     
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  16. Update:
    Well I took the bike out for a ride and also tried revving in neutral and it seems like I can deffinantly get past 7k rpms and most likely redline. Except the vibrations when riding are too strong past the 7k rpms point. So I was thinking with that and the rattling sound it might be that the big end bearings are worn?
     
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