Miilermatic 185......

A couple more things to check are:
Is the spool of wire on upside down?
That could cause undue tension on the rollers causing them to bind the wire as it tries to feed it. Basically, it should be a straight shot through the rollers off the spool. The spool is usually underslung.
Also having the spool not mounted correctly will cause it to bind. It should roll smoothly.
What are your settings?
Too much voltage and not enough wire speed will cause a burn back condition.
Try turning the voltage down a bit and see what happens.
Too much wire speed and not enough voltage will cause the opposite of a burn back, which is ''stubbing'' of the wire while you weld.
If this doesn't do anything, then i bet it's a kinked liner.
Kinked and/or dirty liners will cause a lot of problems overall.
I hope this helps.
Tom.