Lethargic Motorcycle

I am writing to you to seek a solution to the problems that my Honda CBR 250R has been beset by. Earlier, my bike used to have good acceleration and top speed. Nowadays, however, it doesn’t attain the same top speed. I have changed the oil-filter, fuel-filter, chain and sprocket but the bike still doesn’t go to the earlier top speed. Earlier, I could do the top speed in sixth gear at just 6,000–7,000 RPM; now I have rev the bike harder to get to that top speed. Furthermore, the engine feels stressed whenever I try to get to the top speed. Another problem is that the front brake has become quite weak compared to what it used to be earlier. I have replaced the pads twice, but it still feels weak. Please advise me.

Shivam, via e-mail