Some updates....

I have found 5 minutes runtime. After some tests with the 2031 exhaust I could reach 4:50 on a tank. Changed the pipe to a 2015 with the 6 fin header and added some volume to my tank, it seemed a few cc to small and now I can reach 5:15 easy.

My 1st engine has about 13 liter use and now the main bearing seems to be failing. Meanwhile I have changed the rod twice and have used a R7 instead of a R4. No performance issues with that.

I started to use my 2nd engine because the 1st needed a rod replacement and I had no time for it. The performance, milage and temperature is exactly the same as my 1st one. Sadly in the 1st race at the end of a final it started to rain and I had to drive on. The engine had seen 10 minuts of rain and afterwards the standard procedure to let it idle for a while and stop th engine by dripping some afterrun into the carburator. A week later with a start the bearing was noisy and with an inspection it had lots of rust.
This explains why I can run longer on a bearing than I am used to be, bearings that rust less fast have softer races.
I changed the bearing for a normal steel one (#16800) and again no performance issues.

The performance of my 9CL is noticed and some people have bought one as well and are very satisfied with it. One guy copied the timings into an ISON21 and that one is performing the same. (the base of the 9CL seems to be an ISON21)