Hello there. I'm new here so would like to introduce myself at the beginning. My name is Roman and I am happy owner of CBR 600 F4i.
The reason why I'm here is that my baby is acting kind of weird.
Up to 6000rpm lets say it goes normally, accelerates and everything, between 6 and 8 000rpm there is hole- bike turns in to lazy machine, generates low tone sound ( like would get too much air) and its very difficult to speed up. Once engine reaches 8000rpm it goes really really fast and accelerate I was told better than it should. I went to garage and guy after having ride and checking air filters and all hoses around air box told me that bike has been modified. I forgot to mention that it also consume quite a lot of petrol. On full tank (18l) i will do around 100miles and i am not rushing bike at all. My question is what kind of modifications could cause such behavior? Mechanic told me that whole power has been moved in to higher rpms. Previous owner is not willing to give me any information about bike so maybe someone had similar experience. I am using it daily to commute in the city so race performance its not something what I am after.
I'll be very grateful for help. cheers

 

Welcome to CBRF Roman! Congrats on getting your F4i.

The F4i should easily get 150+ on a tank of gas. So at your reported 100 mi, there is obviously something changed or affected. Why can't the 'mechanic' tell you what's been done?...I mean, after all, he's a mechanic right? He's got it right there to inspect. As far as the previous owner NOT giving you info on the bike... That does not make sense. Why not??? You didn't get any service records or research the bike b/f the purchase?

Just trying to get a clearer picture of what's going on.

Hope you/we can get it figured out.

 

after that quick inspection he said that most likely timing shafts has been changed or it is possible that timing has been adjusted by one tooth and it's not worth it to change that back (if timing shafts has been changed). Easier to sell and get new bike. After the ride he said that front wheel goes up on third gear by opening gas and that is not normal for this bike. So i believe modifications are serious. To be very honest when I was buying this bike I didn't know what to expect. It's my first CBR and first bike with injectors so I expected that there will be some difference as I changed from fazer 600.

 

Not sure about what this 'mechanic' is telling you. Is he a factory Honda certified mechanic at a Honda dealership?

What's the story w/ the seller *not* giving info?

What are the sprocket sizes on the bike? Oem is 16/46. Sounds like if you can pull the front end up in 3rd that you are prob running something other than oem sizes, like -1/+2 or 3.

Does the bike run at normal temp range or other?