Folks,
I'm 6'5", I have been racing karts and been involved in karting since the early 1960's. The last kart I raced was ZIP Bandit with a modified PCR 135cc reed valve engine. I had the front porch of the kart extended about 4". But I was racing Long-Track events, so the rules were prety different than sprints. Don't let tall get in your way, but try too keep your weight down and fitness up as much as possible. Karts give you a real workout.
John Skuja
Crew Chief
OFR Extreme SuperKarts
http://www.ravens-roost.com/ofr/ofr.html