I have a 2010 Bolen model: 13WC762Fo65/ 317737/ 38" cut/13.5 h.p./ 334cc/ engine specs: Powerbuilt Briggs and Stratton model 21B807/ type 2453 B2/ code 100528ZA. more engine specs: ABSXS.3442VM 279216 family:EU E1197/68SA. Now here's my problem. When I started it yesterday, it backfired through the exhaust non stop . It was a loud ear piercing popping sound. One valve is not moving as the other valve. I was told to check for a bent push rod. I removed the push rod and it has a very small bend, it is the non magnetic push rod, I believe it's the intake side, the lower rocker. I am aware that a bent rod will cause problems, but does it sound like it could be my problem? And after I install the rocker can I then push on rod and turn over engine to check for cam damage? If the push rod does"t attempt to move can I then assume the cam is bad? I have a couple more questions. If cam is bad should I replace the whole engine or replace the cam in this engine? If the nylon lobe on the cam is the problem do they make an aftermarket all steel cam? Thanks again. Scott Walker