hello
im having a little problem with my bike. When the bike reaches 5000rpm it hesitates and i have to open the throttle fully to ride throught the problem and then it revs cleanly as normal above 8000rpm. I thought it may have sumthin to do with not enough air getting to the carbs so i done a few moifications, but it is still the same. Could it be the powervalves or carb jets, if it sounds like carb jets what jets would be best? The bike is standard apart from exspansion chambers and wire splice.

any suggestions would be greatful

i get similar probs when my nsr150 is cold. (just needs to be ridden out - try not to over rev when cold).
u said u have probs when u reach 5000rpm, what about when below that?
a hunch tells me that you are running lean... but u didnt note any over heating problems...?
also check the sparkies to see their condition..
what mods did u do and what wires did u splice??