apache rlx 100cc quad,loses power?

hope someone can help,ive recently purchased this quad for my son,it starts fine and runs very well on full throttle from cold for approx. 7/8 mins,then it seems to lose power when you try to give it some throttle,although it ticks over lovely.new carb and coil has been fitted,and fuel lines have been checked.if I turn it off for 10mins it will run fine again for a couple of mins but not as long as if it was left for a few hours.could the carb be blocked?can anyone help please?