need help

[ryan 83]

We have a 2003 polaris 90 my son rode for about an hour wed. evening we put it in the garage when finished. On sat. he was getting ready for a ride and it will not start. It has gas and is getting gas to the carb,it has spark ,but appears alittle weak I put a new plug in it still about the same. Can anyone help me out? I am about done with the mini quads!!!!!!!!!!!

Thanks ,Keith