Slide Stop Doesn't Pop Up

The only problem I had with my new to me carbine is when I depressed the slide stop it didn't pop back up when the slide was pulled to the rear.I had to tap on it to get the bolt to close. I disassembled it to find the spring full of sludge so I cleaned the old spring because the new one I bought seemed to be way too long. When I got it back together I still had the same problem. I just don't understand what force makes it return to it's up position.The spring creates friction from the side and there is no return spring pushing up. I can surely live without it but would like it to work and would like mostly to understand how it's supposed to return up when there is nothing pushing it there.. Thanks for your time

 Thanks so much..I see the ramp now in the stop catch hole and now that all the gunk is cleaned from the spring and around the stop it's functioning as designed. I was trying to make it pop up while the slide was off the gun wondering why it didn't.. (duhhh)