Here's a clip from the 1979 movie: Captain America II: Death Too Soon. Unless they dubbed the sound in, he's definitely riding something Japanese. This clip is kinda long, but you've got to watch it all the way to the end, cause he drives off a wall and pops out a hang-gliding rig and goes sailing away, bike and all. Very cheesy. btw, this was filmed at Folsom Prison.
The Captain America motorcycle, under all that fiberglass and dust, is one of the great bikes of all time. In the film, it sports a ripping GP soundtrack, apparently in an effort to justify the GP-style exhausts hanging out of the fiberglass tail. The machine underneath is a Yamaha TT-500, a snapping and snorting two-valve single. The Real Captain America Gary Davis - Web Originals - Road & Track