Why is my lawn mower clogging up?

It is a Snapper lawn mower with a bag. But very little seems to be getting to the bag. The blade is not on backwards and not bent. I sharpened it. There is no obstruction in the chute other than grass. These were foot high weeds but I cut them down first with a weed wacker. My other Snapper did not clog up this way doing the same job.