Hello and thanks for your answers.
I would agree with you in most cases and I would do the same assumptions. However, I have to say that most of the things you describe are not valid in my case. More specifically, the engine is not lean, I have good smoke all down the straight and when I enter the pit lane it idles properly for ever. Therefore, I believe that temperature is not an issue. I have seen other engines starting easily much hotter than that.
The engine is very competitive and still the piston locks on the upper side of the sleeve. The same thing happened since day 1.
That is why I am going crazy.
Thanks again