I still need more patience to tune the carb properly, 'cos it's an airbleed carb and i simply hate it.... But i only managed a better idle (still high) with the airbleed screw almost out of the carb body!
I went to my workshop an hour ago and picked up the engine, just for picking it up sake. Then I noticed that a notch on the engine block is touching the head lip, and that's for sure why it doesn't seal up properly. I'll try adding a second gasket and report.
It's always interesting fiddling with different engines to learn and for others to have a "base" if one wants to "mess around" It's part of our hobby!

Here a video of the engine before the mods, with the same prop and fuel taken 5 days ago:

http://www.youtube.com/watch?v=TXlmI9mXZyw