Check the open circuit voltage of the power source, it should be at least 70 to 80 volts if you are using low hydrogen electrodes. Also, check what kind of electrodes are there with you. Do not bake them if they are cellulose coated.
The leads may not be a problem as you said that once the arc is struck, the machine works fine. You may infact check your electrode coating chamfer at the striking end. if the chamfer is not proper, you will not get a good start.