I have an idea: I once had the same thing happen to me - with the same engine as it happens. I'd switched the fuel lines, i.e. fuel was being taken from the tube without the clunk. This meant it ran on the ground normally (not lean) as it was still able to get fuel from the top of the full tank, but when the nose went up for takeoff the fuel ran back and let it go lean until dead, several seconds later.

It happened twice before I left the field and thought of it driving home. Quickly verified at home.

Worth checking. That engine has modest power, but runs very well.

PD.