I never got to ride a yz490,but hear they hit hard and a kx doesnt have as much hit down low.But if you time it right, power to body english you can wheelie anything,even a bicycle.Try to pull up on the bars as you get on the gas,and you may need more time on the kx to get used to it,it sounds like your trying to ride it like your 490.And this is if your bikes running right,is your jetting correct or your clutch slipping?I dont have any problems getting the front tire up on my kx500 is why I ask,good luck.