When running at high speed smy f2 seems to stop giving power, but gives plenty of power getting to 120 then nothing! Iv changed and cleaned carbs, she idles fine no flickering of the idle needle, shes got a straight thru yoshi end can, standard air filter am i missing anything? Thanks

 

Even though you've cleaned the carbs I'm still leaning towards crap in the main jets. It can be tight in there and sometimes you can't even see it before running a strain from an electric wire back and forth through the jet. Possibly wouldn't hurt to put one notch bigger jets in with that yoshi.

 

New set of carbs were taken from a working bike, i changed the carbs as i thought the problem im getting was due to the carbs but i still have the same issue with these. What size jet would i need? What will i have to set if rejetting?

 

https://cbrforum.com/forum/f2-tech-9...atabase-81653/

See if that helps. You first have to know what you got before you can upgrade. Do you remember do you have fixed clips in your jet needles or do you have several grooves you can put the clip? If so, raising the needles (putting the clips one groove lower) might be enough since the problem is only at full blast.

 

Beside the main jet possible being clogged, you may not be getting enough fuel into the bowls to sustain such speed. Make sure your filter is not clogged or restrictive and you've cleaned all lines leading to the bowls. The F2 is gravity feed so the fuel supply to the carbs must not be restricted in anyway.

Another possibility is your sprockets. Are you sure its bogging down and the previous owner didn't just put over sized rear sprockets with a smaller front? depending on the size of the sprockets the bike can tap out at 120 and it sometime feel like it's bogging down but in reality the gearing have reached the maximum speed possible

The ignition system can also produce such a feeling. I would check the coils pack resistance to make sure that they are within spec. A faulty coil pack can make the bike feel as if it have a fuel issue when in reality it's a spark problem.

Last possibility is how the bike is bogging down. Sometime at higher RPM's, excess vibration cause faulty safety switch to activate causing the bike to lose spark thus bogging down until the safety switch can go back to the proper state of function, after some vibration is reduced. You have to access how the bogging is taking place and begin checking the system from most logical to least logical possibility. Check the easy stuff first to not get into a situation where you've taken the bike apart and the fix end up being a simple one.

Sab