Sounds like the clutch is not releasing. I picked up an HR215 with similar symptoms, the BBC was clogged with grass.

Canguy: Thank you for the input.

I checked and cleaned the clutch area, lubricated all the springs and linkage. However, the clutch still automatic engaged whenever the engine runs. This is very dangerous condition.

I tried to remove the clutch but the nut just turns with the shaft. Somehow I have to lock the shaft to remove the nut.

May be the clutch needs to be replaced . What do you think?

Blade "brake/clutch" is out of adjustment, or worn out. Pulls a little harder because the blade is always spinning. When you release the self-propell handle, the blade continues spinning. CHEAp fix which I have done to my HR214 is to use a nylon cable-tie, pull the blade engage lever "on", and tie it into that position. Been running it that way for years. jUST BE AWARE THAT THE BLADE IS always ENGAGED!!!!!

Blade is is upside down.