Justin Bieber is breaking down, y'all ... his bike, that is. The singer had some mechanical trouble with the new custom Drew House-embellished motorcycle on Saturday as he tried to take the motocross machine for a spin around Beverly Hills.

As he pulled up to the stop sign at the beginning of his cul-de-sac, the bike conked out and made some really weird noises, but Justin got it going again after revving the engine a few times. And then it was off! Biebs took a spin around Beverly Hills, escorted by two of his bodyguards in two different SUVs -- one in front, one behind. Hey, a pop star's gotta be careful!