There's an easy fix to stop that which we used to do back in the day when we used to run 14.5:1 compression upto 12,000 rpm on our 150mph C11 and C15s. You go out in the woods on a dark but moonlit night with a good bowsaw, you find a nice oak tree, saw off a lump of oak about a foot long and 6 inches thick, take it home and leave it near a heater for about 3 years. Then, you shape it into a nice wedge, remove the tank from your C11 and bash the oak wedge in between the rocker box and the frame until the frame just starts to bend. Then you get the Hilti gun and fire a few nails through the top tube into the oak and there you go. It'll never come off again. It stops all that annoying agro when you are burning some kid on his R1 off at the lights. The additional weight of the oak helps to keep the front wheel down coming out of fast corners. you dont need any anti - wheelie devices on those babies.