Not sure then, but it shouldn't need a bigger jet unless someone added a pipe and air filter or messed with the jets before. Pull the gas hose off the carb and make sure gas is flowing from the tank good. Also, check to make sure your gas cap vent isn't clogged. If putting the choke on, makes it pick back up and run good, then you're definitely not getting enough fuel for some reason.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.