Hey guys, I am new to the forum so please go easy on me. I recently purchased a very nice Huskee rider for $100.00. The reason for the ridiculous price is that the engine does not sound right. It has a 17.5 h.p. briggs & stratton ohv engine, and when started it sounds exceedingly loud, and just not right. Upon close examination, (and removal of the breather)I discovered that the extra sound was coming through the carburetor. I can literally feel the exhaust coming out of it. My first thought was it has to be coming back through the valves, so they must be burnt(or at least the exhaust valve) I removed the head, and turned it on its side and poured a little gasoline in it, and sure enough, I had leakage. I removed the valves from the head and cleaned them up, and re-installed, and re-tested. This time no gas leaked past the valves, so I re-assembled everything, and adjusted the valve lash per Briggs & Stratton specs. The problem still persists with no change. My next thought was the muffler could be in some way plugged, causing back pressure so great that it would push the exhaust valve open and come back through. I disconnected the pipe from the muffler, made sure that it was clear, and installed it pointing up, instead of into the muffler. When started, it still had exhaust shooting out of the carburetor. I looked at the flywheel key, and it appears to be o.k. I have fixed many a lawn mower in my time, but I have never run across anything of this nature. Any suggestions? or has anybody seen this before? Thanks in advance for any help you may be able to offer.