Motorcycle Repair: carbs, computer issue, throttle control

Question
No i did not take the carbs apart. took bike to a yamaha shop they said the carbs were fine. I noticed the other day, with the ignition key turned on, but bike not running, the rpm gage woud go from 0 to 8000 then back to 0, it would repeat every 10 seconds.
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Followup To

Question -
2001 yamaha yzf 600r.  Bike was hit from side and I had to put a new motor in, used the carbs from the old motor.  I can not get the bike to go over 80mph.  Around 50mph the bike will speed up a little then it acts like it is not firing all the time.  When I get it to 80mph the speed will drop down to 65mph then jump and lunge back up to 80mph.  The entire time the throttle is being held wide open.  It acts like it dont have the power to pull a load. When going up a hill it dont have any power. I was told it might be the CDI box.  Or the throttle control sensor.

Answer -
It could b those parts, but I have a question 1st.  Did u seperate the carbs into individual pieces at any time?  Have u cleaned the carbs?

Answer
One more question, r we sure this isn't a fuel injected bike?  This sounds like a computer issue to me, but if it's carbed then that's not the case.  As to the RPM guage I would suggest calling a dealer 2 c if that's normal as I can't diagnos without the bike.  If this is a carbed bike u either have a timing issue, or the bike is running VERY rich.