Why does my motorcycle smoke?

The father leaves, and the brothers go for a long motorcycle ride through the city and enjoy a few smiles along the way, although The Motorcycle Boy's reckless driving frightens Rusty James here and there. They arrive at the Pet Store, and despite Rusty James' pleas, The Motorcycle Boy breaks in and starts to set the animals loose. Rusty James makes a last-gasp effort to convince his brother to start acting more "normal" and reunite with him, but The Motorcycle Boy refuses, knowing they are too different to ever have the life Rusty James speaks of - something that causes Rusty James much pain. The Motorcycle Boy then tells Rusty James that, whatever happens, to take his newly stolen motorcycle all the way to the ocean. The Motorcycle Boy leaves the store with the Rumble Fish, but never makes it to the river. Patterson meets him before he can dump the fish and shoots The Motorcycle Boy, killing him. Rusty James is too late to stop the shooting, but does complete his brother's task and get the fish into water. All the major characters congregate at the scene and see The Motorcycle Boy has been killed. Then, as Coppola's very lengthy "reaction" shot ends, we see a motorcycle shadow racing across a slab of concrete where the words "The Motorcycle Boy Reigns" is spraypainted. The movie ends with Rusty James finally reaching the ocean, where the sun is shining.