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Mike Vick has finally selected his new jersey number -- #8 -- and sources connected to the NY Jets quarterback tell TMZ Sports it's all because of Steve Young.

As we previously reported, Vick decided NOT to go after #7 -- the number he's rocked since high school -- because Geno Smith wore it last year and he didn't want to start a controversy behind the scenes.

Vick posted on his Instagram this morning -- saying, "I want to see everybody in there MV8 jerseys this year. I appreciate all the fans that helped. Fresh start..new me! #JetsNation #GangGreen #V8."

Our sources tell us ... Young was a HUGE factor in the number selection because Vick has always looked up to Steve ... "He's one of Mike's favorite players of all time. Also, he's a lefty, too."