Justin Bieber -- Blazin' Again ... But Not Like That

Justin Bieber was caught speeding in the valley and it's cost him thousands ... which is just how he planned it.

Biebs was down for a little late night go-kart action Wednesday night for a bud's b-day ... and dropped a few grand for an after-hours, all-access adrenaline session at MB2 Raceway.

We're told ... JB arrived with a dozen friends -- including Hailey Baldwin. We're told he dropped $2,700 ... the cost of burning rubber for 2 hours.

The staff gladly stuck around ... Justin threw them an extra $500.