Writing Multi-chapter Stories

When it comes to writing stories, I think of myself as a sprinter. I'll get burst of creative energy, but tend to feel winded by the time I've reached the end a story. I think I've only written a story with over a dozen chapters once. But ... I do find there's times when I enjoy writing multi-chapter stories. I just wish I had more stamina for them.

So, for anyone who's written longer stories, where do you get the stamina to stay with them for more than a few chapters?