I have a walk behind mower that is set up to mulch. Lately it seems like the mulching is not happening. I figure after a year it was time to sharpen the blade. I sharpened the obvious part of the blade that needed to be sharpened. My question, is there a secondary part on the blade that needs to be sharpened? The grass that is being put back on the lawn is no shorter than it would be if I discharged it out the side. It used to work better. I should add it was a 3 in 1 mower. I did not add a kit to it or anything like that.