I did a rebuild on my unit, new piston rings, gaskets, timing chain, tensioner. Everything is torqued to specification. I can not get it to start, I have spark constant, good compression, Air flow, fuel but it will not fire. Pour gas down the hole and still no joy.I did not remove the carb or disconnect the fuel lines, valves clearance is at 0.006", the camshaft decompression is in correct placement. I bought another known h good engine and it's the same result... No joy. Is there something I am missing, or something obvious that would be seen by fresh eyes?