This is my first post, I hope I wish I came here sooner...
I own a Sears Craftsman DGT6000 with a Kohler 27HP (175hrs, 7 yrs old). It started making a huge backfire thru the carb. I checked compression, cylinder 1 = 150, cylinder 2 = 0. I pulled the head on cylinder 2 and discovered the hydraulic lifters were frozen wide open. I removed them and cleaned them internally, black tar came out of both, I suspect the holes got plugged and the oil was stuck inside. I put the lifters back in and now I had 150 compression on both! I noticed the exhaust lifter was not moving much, the engine sounded perfect at idle, then I when took it over 1800 rpm it would begin back firing thru the carb. I pulled the engine out and cracked the case open, the cam was worn down to a small bump for this exaust lifter. I replaced the cam (matching the dots on the cam & crank). Now it wont even try to start! I have replaced all four push rods, a couple were slightly bent, not seen by the naked eye, they wobled when I rolled them on a flat surface. I also replaced both valves on cylinder 2, just in case the stems were slightly bent. Still no cigar!, All it does is turn over and it will have a light back fire (puff/spit) out the carb when I close then open the choke.
I have pulled the engine out two more times, once to spin the cam 180 degrees (even though the service manual makes no mention of TDC). Another to confirm the cam lobes match up to the old one and to have a certified mechanic confirm the timing looks right. This has me baffled, it ran, though be it crappy, it ran w/a bad cam, lifters, push rods, and valves. Now, it is all replaced and doesnt even try. Please help, before I take a baseball bat to this thing!