Reply To: My motorcycle loses power at high RPMs and full throttle – Hyosung GTR
The intake pipes won’t be a problem 5% is loss of power is like 1-2bhp but it is not a big deal, i would focus in getting more air via an improved intake like K&N Catridge box or try BMC air filter (Since you are close to italy , find a local distributor that imports BMC filters as they are a little better than K&N, just a little – Just ask them for Carb Model GT250/GT650)
Exhaust headers = it is possible it will be restricting exhaust flow a little bit! = I would try to get OEM GT250 headers and use a full size muffler/silence with DB Killer
We don’t know the muffler you have, so i am guessing at this point, but yes 125cc headers will need changing so it breathes more easier at higher rpm.