I run a TNX with the similar engine. I also initially had some overheating issues but was able to overcome them.

I was running 240 degrees until I opened up a hole in the windshield and opened up the side window. Not sure if you have done this? My temps dropped instantly to 199 degrees with the same settings!

Seems the OS 18 likes cool air on the head.............maybe why the TNX pro comes with a larger head? Mine with the stock head runs 100% now

Hope this helps

Lenny