2000 Posts and climbing!!!
Join Date: Oct 2009
Your English isn’t ‘poor’ at all. The HT-20 has an in-line Sundstrand 15 series transmission. It consists of a piston pump directly coupled to a piston motor. What’s happening is the motor is spinning faster and using more flow than the pump is producing. It’s cavitating; which is very bad for motor.
You should rev engine to maximum (governed) speed, while keeping speed control treadle low.
Or, use brakes.
Girls with large lawns like a guy with a really big deck!