Belt keeps mower in motion

I have been building a racing mower and have only test drove it two or three times. The belt is loose when i push in the clutch, and is pretty dang tight when the clutch is out. But the belt is still grabbing on the rear pulley causing it to creep forward when the clutch is engaged. Any help would be greatly appreciated.

Maybe adding belt keepers would do the trick to stop the creep?

Thanks

gonna need a bigger belt. I have the same problem. Sux, but whattaya gonna do?

What pulleys do you have? Belt keepers won't fix the problem, either the clutch isn't giving it slack, or the belt is a hair to short. Maybe a few pictures might help. I've had better clutching experience with 1/2" belts then 5/8"

If you smaller idlers for the system that might make it work.