In more ways than one, Tamar Halpern and Chris Quilty’s documentary “Llyn Foulkes One Man Band” is about not knowing when to stop. The filmmakers are blessed and cursed with a subject who seems to lack the usual filters. We, in turn, witness Foulkes in action, at length — revamping his works, railing against the art world and speaking his neurotic mind.

Now 79, he belongs to the constellation of West Coast artists in the 1950s and ’60s widely associated with Pop. That’s only part of a career featuring junk assemblage, geological portraiture and a sideline in music with a homemade Seussian contraption of horns and drums. He comes across as a mostly lovable, cranky and brilliant outsider who nurses a gallery-size chip on his shoulder about not getting his due.

Perhaps too obediently, Halpern and Quilty adopt the not uncommon narrative of a comeback, building up to a New York exhibition and coming down with Foulkes’ ensuing recovery period. (The film covers seven years in all and includes Dennis Hopper among its interviewees.)

The idea of a work in progress is vigorously exercised before our eyes: Foulkes adjusts elements of his textured, wall-size piece “The Lost Frontier” and saws off an offending portion of his painting “The Awakening,” influenced by a past marriage.

His self-edits demystify the sanctity of completed artwork and serve to produce a mix of hope and terror among any chronic procrastinators in the audience. It’s part of a glimpse of creative excess matched by cutaways and clips of Foulkes’ songs, and his hopefully cathartic stream of musings, regrets and complaints.

Halpern (who has made fiction films, including “Your Name Here,” featuring Foulkes) and Quilty face a common pitfall: a reluctance to rein in a personality. Maybe it arises from a belief in the authenticity of an unmediated voice, or maybe just from growing accustomed to his routine. But Foulkes overwhelms this documentary, which buys into his one-man band a little too much.