I have a Craftsman DHS with a Briggs 20 hp. Engine turns over, has spark, new plug, plug is wet, so it is getting gas, checked flywheel key, not sheared. Mower was running turned key off, 15 mins. later wont start. While turning motor over with plug out spark appears to be a little on the weak side. I had flywheel off to check key and shine.d the maganent up. Anybody have any ideas what to do next?