Hi Dmitr,
Well done problem solved! I knew it's not an easy fix as we need to pull the motor off to access the nozzle. Just to share to share to everyone why it's the vacuum nozzle would be the problem.
How this vacuum nozzle works?
First when the flywheel spins and blows air past the nozzle, it will create a venturi effect which caused vacuum which restrict the movement of vibration of the diaphragm. The higher the RPM, the higher the vacuum and the more movement restriction on the diaphragm which tends to slow down the engine. This close loop feedback or we called it governor will maintain the speed of the engine regardless of the load.
I will demonstrate this effect in one of my YouTube video for others to have a clear understanding.
Cheers,
CM
