Comet II not feeding

[mgmine]

Hi I just bought a Comet II and have no idea why it's not working so I did a search and was amazed to find a web site dedicated to these machines! The problem I'm having is that the balls don't get down to the part where the flipper handle is. What happens is they roll down to the center of the machine (in the back) and then don't go anywhere they just back up. After I pull some rods and move some of the plastic stops they empty out through the bottom. Here is a picture of where they are jamming I have removed a plastic cover so that the the balls can be seen. I don't want to just start tearing into things and messing the thing up when it might just be a simple problem Thanks for any help.