Walk Behind Lawn Mowers

I bought a Sam's Black Max mower mid summer of 2012. Checked/operated about 15 minutes. Stored in basement remainder of 2012. Began to use summer of 2013. Cutting grass, I pulled the mower backwards to change direction & heard a loud noise. I released the handle-control. Eng stopped. Examined. The foot guard was cut to bits. Why did it make contact with the blade? Was the part "too big", improperly installed, or why did this happen during normal use? How do I obtain a replacement for the molded plastic part used for the foot guard? Also, is there an easy way to modify the engine so I can control speed vs running wide open full time? Thank you. Gerald Mason, 2232 Ridge Wood Ct. Marietta, GA 30066 (H)770 973 6390