How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Louie Your Own Question
Louie, Technician
Category: Motorcycle
Satisfied Customers: 12318
Experience:  25+ yrs. experience
Type Your Motorcycle Question Here...
Louie is online now
A new question is answered every 9 seconds

I have a 2000 CBR 600 F4, its a california model and

Customer Question

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 9k-10k...";
  • • and/or if able, try with the needles raised by 1 notch and note if also any change in the "...hesitation/flat 9k-10k..."

Related Motorcycle Questions