A quick method for setting the feed roller tension, is if you block the nozzle to stop the wire coming out (bend the end over and hold it with your finger against the tip is enough), the rollers should spin on the wire.

If you set the tension too high, and the nozzle does block (you'll probably do it a lot to start with due to burn back!), you risk ending up with the wire kinking (or a full blown birds nest if you stupid enough to keep holding the trigger!) before it enters the liner at the feed end.