z50 will not hit

hello guys, I have a 1979 z50, put new stator on it, got great fire, checked valves ok, an the timimg is on, little slack in timming chain. sprayed gas in cyl. and new plug. put finger over spark plug hole has compression, how low does the compression have to get before it will not run. thanks for the help. Joe

hello guys, somehow my location wound up being afganistan, don't know how that happen, it ain't here in mississippi.