A little history to start, this motor has only 70 hours on it. I just put it back together from fixing a seized rod journal. After a few hours of mowing the yard I was out front finishing up cutting the ditch (sidehilling) and the motor stopped abrupbtly with a bang and a clatter, after teardown I found the rod had seized to the crank and snapped. I've replaced both and cleaned it out, the wierd thing is I'd recently checked the oil and it was fine but I only found about half a quart in it when I tore it down, not enough to splash when it was on the sidehill. I also found the headgasket was blown into the pushrod cavity while I had it apart, mabye that's where the oil went? Plug was clean and dry, it wasn't smoking at all. It started perfect the first time after reassembly and after a quick adjustment to the governer (had to loosen it to get the crank and silly AVS weight doohicky out of the case) I had it purring along for about a minute. I shut it down to finish bolting on the cowl and fuel pump, and now it won't hardly run at all. It's getting fuel no problem, I've already tried pouring extra gas in the intake to no effect. It is also backfiring both through the exhaust AND through the intake. I've checked the valves are ok and adjusted, it is generating plenty of compression, spark is strong. Opened the case back up and verified timing marks align and everything in there was still kosher. I also went through the carb and blew out all of the orifices, no gunk or anything in there. What the @#$@# could it be? I'm about ready to roll this damned POS mower off a cliff. I'm going on 3 weeks of growth now, going to have to borrow the neighbor's tractor and brush hog. Help!