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Louie
Louie, Technician
Category: Motorcycle
Satisfied Customers: 11451
Experience:  25+ yrs. experience
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I have a 2000 CBR 600 F4, its a california model and

Customer Question

Hello!
I have a 2000 CBR 600 F4, its a california model and carbureted.
I am experiencing a hesitation/flat spot. It is most noticeable at 9k-10k wot. The engine seems a bit soft around 8k and cleans up after 10k ,6th gear wot. I can achieve stronger acceleration with less than full throttle.
This bike is not stock, i have replaced the cams with 49 state cams and black box, a factory pro jet kit and needles, two brothers headers and a yoshimura ehaust, bmc race air filter. I have other parts, but these are the ones that i think are relevant.
I have removed the pair valves and replaced with block off plates. I have also replaced the 2 stage ram air carb vents and vented directly to the airbox.
Any thoughts?
Submitted: 1 year ago.
Category: Motorcycle
Expert:  Louie replied 1 year ago.

Hi and welcome to JustAnswer,

Thank you for the question and your patience. Should you still need assistance for information purposes only...

Initially, proposed preliminary considerations (if have not been factored in):

  • • check sparkplug tip burn color;
  • • if light brown to whitish, then lean and/or a very small air leak concern;
  • • try adding an add-on/top layer of foam sheet to the air-filter and note if any change in the "...hesitation/flat spot...at 9k-10k...";
  • • and/or if able, try with the needles raised by 1 notch and note if also any change in the "...hesitation/flat spot...at 9k-10k..."