This example from welding could provide the solution you need.

http://www.fabricatingandmetalworking.com/2011/08/troublesho...

Commonly referred to as a bird nest, the welding wire can get backed up and tangled among the drive rolls as a result of a blockage in the liner, a contact tip burn back or improperly adjusted drive rolls.


http://www.assemblymag.com/articles/86511-troubleshooting-th...
All About Wire
Wire feed stoppages and wire feed system malfunctions can adversely affect the welding arc and create irregularities that may weaken the weld bead. Bird nests -a tangle of wire that halts the wire from being fed-is a common problem. You can resolve bird nests by flipping up the drive roll and pulling the wire back out of the gun. Next, trim the affected wire and rethread it through the feeder and back to the gun. If the welding specifications allow, decrease the drive roll tension, use a larger diameter wire and reduce the distance the wire feeds to minimize the chance of bird nests.


"Drive roll tension should be adjusted so that it is not too tight, but not too loose. Start with the drive roll pressure very loose. Increase the pressure only until it is very difficult to stop the wire from feeding out of the contact tip. Use a pliers or block of wood to try and stop the wire from feeding. Go perhaps one-half of a turn beyond this point. When the wire is actually stopped, the drive rolls should spin on the wire and no bird nesting should occur."