so i did it yesterday, and it was a success
first i changed the battery poles, that were mistaken, and then checked the polarity in the coil, now terminal 15 is positive and 1 is negative, alles in ordnung !
then i rechecked the points gap: is 0,3mm without advance and 0,5mm when maximum advance
then checked for TDC using a plastic rod throught the spark plug hole, it was a bit empirical thoug, but i was able to make a painted mark in the flywheel, so i knew where i was
then using my other engine that is disassembled i set the piston stopper at 9,5mm: i removed the cyl head and place the piston at 9,5mm BTDC, then i adjusted the piston stopper accordingly
i went to the motorcycle and placed the piston stopper in place in the running engine
i slowly moved the piston until it stopped, i made a mark in the flywheel for a 9,5mm BTDC
using my 6 volts red light (a diode, so it has polarity) i connected it: black cable to ground and positive to the condenser terminal in the ignition module (at last that now polarity is correct:_)
placed the lever in the handlebar at maximum advance, so ignition module is set at max advance (remember that this is moving the points anti-clock wise)
then using the cable adjuster of the ignition module i tuned the position of maximum advance so the red light (and thus the spark) was just switched on in that position of the crankshaft (9,5mm BTDC)
once done i removed the piston stop and rechecked:
1- with maximum advance i checked that the red light just switches ON (spark firing) when passing through the 9,5mm mark in the flywheel
2- now i put no advance with the lever in the handlebar
3- i checked when the spark is produced in this condition, and i found that spark ignites AFTER TDC !!! only a few degrees but ATDC, surprising !
and finally i started the engine, wow, so loovely !
no knocking at all, started very well, i assume also new points and new condenser where part of it !
thank you all very very much, now i understand my motorcycle (it has been 10 years ;-))
...it will continue ...