Hey people I'm looking at a 2005 CBR600F4i and I'd like to know what are the most common problems with these bikes?

What is the weakest performing part on them?

What should be the first upgrade in the name of performance?
It could be brakes or engine related.

Rider upgrade is a necessity

 

Sorry to jump all over your posts but I'm at work (lol) and I'm bored
Common problems would include:
CCT (cam chain tensioner) - This is probably the most talked about. Although it is really not a mechanical issue which would cause engine damage, they do on occasion have a tendency to become noisy. The noise becoming only obviously apparent through certain RPM ranges thus leading some persons to believe there is something seriously wrong with the internals. Easy fix however.
FPR (fuel pressure regulator) - This will cause various running issues including not starting, poor idle or poor performance at higher rpms. Again, a moderately easy fix.
Voltage Regulator/Rectifier - This one is not as common as the top two but it is worth mentioning. Problems with this will cause the battery to not be re-charged during operation thus causing the battery to fail, most notably (obviously) during start-up. Also an easy fix.

As far as upgrades, gearing ratio changes are easy and inexpensive. This involves simply changing your chain sprokets to different number of teeth such as -1/+2 (minus one tooth in front, plus two in rear). Further up money wise, a full exhaust system with a fuel map programmer would probably be in order.

If you do a search of the problems mentioned above, you'll find plenty of results including diagnosis and repair threads.

 

I wouldnt spend too much time worrying about it. The F4i is built like a tank. the CCT is a common one, but its the only one I have personally had. I have had 2 F4i's, and put them thru hell. Its also the reason the are sought after by stunters.

you could do a sprocket change for a little better bottom end grunt. Or upgrade the brakes for better stopping power.

I think the first most common upgrade is the exhuast, most just replace with a slip on to get rid of the GIGANTIC stock exhaust.

 

If your really concerned about "rider upgrade", you shouldnt worry about performance upgrade till NEXT winter. Get a year (season) under your belt first, "learning" your bike, how she acts and reacts. If your a newb (like me), and dont wanna ride wheelies (yet), then stay away from the -1/+2 sprockets till your comfortable with you bike, the change in ratio makes it easier to lift the front end up (so I've heard). +1 on the "tanks" appearentl they'll last forever if you take care of em. One guy on here has over 100K on his, with the original, not rebuilt motor.