Just because of unreliable and selfish reason I set the ignition timing at 7 degree angle value from BTDC, Toyota EP82 Starlet used at that time had BTDC 10 and Super Beetle 1302 did BTDC 5, so I took median value at 7 degree. And I had been using it for 30,000 km without doubt? Careful checking of the Nul point shown on the crank pulley, I found out additional marking on both side of Null point, probably plus 5 and minus 5 degree marks.
The idea of Anti Pollution was invited at the beginning of 70s and all the manufacturers obliged to delay the ignition timing in order to avoid air pollution all over the world, inhibited gas were Hydrocarbon and Carbon Oxide. As the regulation was applied only on the moment of idling condition, they should do that only on that interval.
VW '71 Super Beetle 11AD had complicated distributore controlling system, advanced ignition timing at 5 degree BTDC while ordinary condition and only while idling moment the timing was delayed 5 degree from Null point. As incredibly very strange and quire timing control was e equipped in the distributor at that era, so the performance of combustion was not always comfortable at all.
As for may Super Beetle, I have been losing the opportunity to set up the combustion timing so precisely as to satisfy myself to enjoy comfortable combustion note, paying attention only on the exhaustion gas inspection done by the Authority.
Remember that the Anti-Pollution Exhaust Gus standard value by the Authority is applied on the manufacturers, not on the automobile users. The regulated standard value for actual users are defined, so vehicle users can do any setting as he or she prefer so far as the specified value of definition should be kept. Probably, differs depend on the country.
Consequently, I applied the value for idling speed, BTDC 5 degree as a testing run, the combination and gradation of vacuum advance and centrifugal advance became far fine and the acceleration smoothness has improved, BTDC 5 degree is Correct as a matter of fact!