The oiler is not working on my Homelite 16" Ranger chainsaw. How do I fix ?

I have disassembled the saw and have exposed the oil port and have cleaned it and the area around it. I have run the saw without the bar, chain, and guides to see if it is pumping oil. When I first did this it did pump oil but when I went to use it, it did not pump oil. I have disassemble it again and have run it and it does not pump oil. I don't know how much farther I need to go or if I can in order to repair the problem. What should be my next step?