Hi Alex,
so it's an A102 - not bad either
Unfortunately I'm not familiar with the A102 engine (my Heinkel is an 103-A1). But I'm quite sure that this engine uses a SIBA generator and a SIBA ignition. So the timing and its setting should be very similar to the settings documented for the 103-A0.
Perhaps one of our 102-specialists can give you better help and exact settings?
You can find the settings for type 103-A0 in the service manual for this type (page 22). It's in German, but I'm sure you can translate it (using translate.google.com or deepl.com for example).
The most important part is:
"The breaker contact distance is: 0.35-0.45 mm. The setting is made for late ignition (centrifugal weights not swung out). It amounts to:0.6-0.8 mm v.o.T., measured with ignition setting device (404/W 10) or 8°-10° v.o.T. Early ignition is carried out at this setting:6.5-7.0 mm v.o.T. or 33°-35° v.o.T. automatically by centrifugal governor." (translated by deepl.com; "v.o.T." means t.d.c in English, which is "Top dead center").
Please keep in mind that type 103-A1 (the one refered to in the only English manual) uses a BOSCH generator and ignition with other settings - I'm quite sure that these would be wrong for your 102.
By the way: I changed the download links in my post from 23.04.2019, they should work now.
If you want to be shown how to set the ignition you can watch some videos at
https://www.youtube.com/user/Heinkelclub/videos. Look for videos with "Zündungseinstellung" in their title. They are in German, but I'm sure you will understand the main points simply by watching.
Please have an additional look at video
https://youtu.be/ZKM6GzRVoZM. There is shown how to test the advance/retard mechanism (using a stroboscope lamp). This is very important for higher RPMs (and could therefore be one possible reason for your problems above 80kph).
A Bing carburator on the old 102 engine? This could very well be the cause for your other problems (high speed as well as low RPMs). It will work (I'm sure) but you have to adjust the carburator settings very meticulously. My personal guess for your problems? Could be a wrong main jet/nozzle (esp. at 80kph and above). Or dirt. Or the accelerator pump (see
https://youtu.be/zZryLQ0O2ng!). Or accumulated dirt in the fuel tap. Or, or, or...
You should disassemble and clean the carburator first (see "Heinkel-Club Service Videos" at
YouTube, search for videos titled "Heinkel-Club Service Video 06" to "Heinkel-Club Service Video 11").
Then you have to do all the carburator settings "from scratch". You can get some very good hints how to do it at
http://pteng.de/heinkel/antrieb/antrieb.htm, part "Vergaser". Again in German only, but deepl.com (for example) gives you a (halfway) reasonable translation.
Have fun and good luck with your 102,
Bernd