After upgrades, Top Speed only 60mph Hawk 250

[DustyRJ7]

I bought a 2019 RPS Hawk for 1k. 3k Miles on the Odometer.

After upgrading to Shinko 705 tires, adding a JFG exhaust, and installing JT 17/45 sprocket combo, my top speed is only 60mph. Also added an iridium spark plug, didn't seem to make a difference.

I checked the oil with the dipstick while the bike is upright, oil level is correct (Shell rotella t4 15w-40)

Everyone claims their hawk does 75mph with these upgrades.

I have not checked the valve clearance, I plan to this weekend. Assuming that the valve clearance is correct, does anyone have any clue as to why a rider at 145lbs is only topping out at 60mph?

My carb is stock, is that what's wrong? Should I order a new engine?

I would really appreciate your guys' input, I am not very knowledgeable when it comes to motorcycle mechanics.