Hi,

A while ago my bike started to act weird.

- when I accelerate slowly form a complete stop it stutters
- riding at stable speed isn't smooth (like the revs would go up and down a bit)
- the bike accelerates fine on first 3 gears to around 80km/h but above that it looses its power. 4th gear almost doesn't accelerate. I tried to accelerate up to 140km/h and then shift to a higher gear but on 5th or 6th it didn't t accelerate at all (even though throlle was fully opened) and was actually slowing down.
- There's a new, weird sound. A humming I didn't hear before but only during load. It doesn't show up while on iddle.

I've checked the air filter - it's ok.
I've used a repair kit for the fuel pump. It rides a little bit more smoothly but still has no power.

So I thought it is the throttle position sensor. I've checked the resistance and according to haynes it should be between 1-6 k Ohm, and icnrease when opening the throttle grip and decrease when closing it. In my case it remains stable all the time at 4,7 Ohm. I checked it on my friend's bike (the same model) and it was the same - resistance stays at the same level all the time.

Do you have any ideas what could it be?

 

Sounds indicative of a vac leak. Have you checked all of your lines and ports on the carbs?