First of all you want to see if the problem is in the steering system or the motor. Disconnect the link arm that connects the steering cable to the engine. Turn the wheel and see how it turns. If it turns easy, try turning the motor by hand, more than likely, it is stiff.
If the wheel still turns hard, remove the cable from the engine, or at least disconnect it and try again. The problem may be in the steering tube on the engine and it might be able to be cleaned and lubricated. Bottom line is to locate the source of the friction prior to throwing any money at the problem.
There is no permanent fix for a tight cable, it has to be replaced. The identification numbers should be molded into the cable housing near the motor end. The new cable will come with the rack on the end, it's four bolts and out it comes.
Make sure you clean out the steering tube and lube everything up good prior to reassembly. It may be less expensiveness to buy a new packaged system than buying the cable alone but you may need to do some alterations to install the new helm.
Good luck