Thanks.  The rotary valve is keyed, it goes only one way.  There is a slot in the back of the valve and it fits on the crankpin extensiton.  Don't think it can be put on wrong.  Engine runs well, it just makes the "cracking" noise.  Yes, I have move the HSN about, the noise does seem to be reduced on the rich side.  Later read through the instructions and noted the direction to richen up the engine an 1/8 of a turn after getting it set up right.  So I suspect the engine is a little on the lean side, but it accelerates very very good. 

Turning a 12 X 8 Master Air Screw K series prop. 

Weather permitting will take it out again.  A very powerful engine.

Chip