Your welcome

I hope it is traced back to your fuel setup. That rules out any problems with the engine and it's an easy fix. Try the viltclunk, the nipple is a bit larger so the chance that you lose it is very small. If you decide to use this clunk, get rid of the filter in your fuel line. 4 strokes can be very critical in performance with any debris, air or obstruction in the fuel (flow).

Good luck!

Great engine by the way, excellent power to weight ratio!

Cheers