If the clutch lever that operates the belt is the large vertical one shown in my picture above, this would mean you have a 430, not a 590 - the 590 has no lever.
If you have a 430, with the clutch lever that tensions the belt, the lever starts and stops the reel and the drum clutch pulley. The drum clutch is connected or disconnected from that pulley by a lever on the handlebar, connected by a Bowden cable to the left side of the drum. If you do not have that control, the machine is incomplete and needs to be fixed. It is not really practical to operate it with the drum clutch permanently locked because you would have to bend forward to the lever, then the machine would bolt when you engaged the belt clutch. Furthermore you need the speed control the drum clutch gives you.
I suggest you post some pictures of your machine, so we can clarify what you have.
