Compression ratio Confusion

Help
i am trying to work out the compression ratio of my EX Mod 109 early 1980`s.
The spark plugs are the 8:1 type but had to set the timing at 6 BTDC to stop pinking at higher revs( no load), this is the 7:1 setting as far as i can tell.

The engine was running well but when checked before servicing( using strobe) the timing was seen to be well advanced I think this was down to a stuck mechanical advance, this was freed up (WD40) and the timing set static at TDC with the resultant pinking.

At present any info i gather just contradicts itself.
The head is the original leaded unit
Thanks
Greg

what about fuel richness could be to lean

the best way to time these things things is by ear.
just use about 6°btdc for geting it started then turn dizzy clockwise abit then anti-clockwise till it just begins to pick up speed.