In its first three sections, “Ode to the West Wind” uses mostly weak end-stops—end-stops that barely register as end-stops. The speaker’s sentences are so long that there are places where it feels like the sentence is coming to a close, that things are finished, wrapping up—but then the sentence keeps going, spilling forward into the next line.
There’s a good example of this in the sentence that starts in line 23, “Thou dirge / of the dying year …” At the end of line 25, the sentence feels more or less grammatically complete. The speaker has called the wind a “dirge” and uses a metaphor to add that night-fall will be like the dome of a “vast sepulchre” hanging over it. (In other words, the night looks like the dome of a big tomb). The reader might reasonably expect the speaker to then move on and say something new about the wind. Instead, in the next line, line 26, the speaker continues to develop the same metaphor—he adds that the tomb is “vaulted” with “all thy congregated might / of vapours.”
That is, the night sky has clouds running across it and those clouds look like the ribs or arches on the inside of the dome. Line 25 is technically end-stopped, but because the sentence spills past that end-stop, it doesn’t feel that way—and so it doesn’t really function as an end-stop: it doesn't introduce the kind of separation between lines that a stronger end-stop would. The poem is so energetic that it simply speeds past boundaries like these. Most of the end-stops in the poem's first three sections work in a similar way: they are technically end-stops, but they don't feel like it. This gives the poem a lot of velocity and energy. Like the wind it describes, it seems to break through all the limitations placed upon it.
In the poem’s final two sections, though, the speaker does start to use end-stops with more strength and conviction—particularly in lines in which the speaker describes himself. Lines 43, 44, 53, and 54 all follow this pattern. Look, for example, at line 43: “If I were a dead leaf thou mightiest bear.” The line is grammatically complete and cut off from the next line, “If I were a swift cloud to fly with thee”—which is also a complete, independent unit. These end-stops emphasize the speaker’s isolation—he wants to be the wind’s “comrade,” to travel with it across the earth. But he can’t. He is isolated, complete on his own—much like the lines that describe him.