Miilermatic 185......

Do you have a tip on the gun? Is it the correct size hole in it? I am not aware of different sized liners, only different size tips.
Are you using, or trying to use gas? In my former welder the feed wheels had two grooves. A smooth groove for using solid mig wire, and a knurled groove for use with flux cored wire.
I'll bet whatever it is will turn out to be simple. You might take it to the welding shop and ask them to look at it.
C