i just got done a nother go kart with a 11hp harber freight engin with 40s tav that weighs 300 400 pounds too and i can make it do wheelies on flat ground il try to post pics
I find that VERY hard to believe, wheelies with that gearing (3.8:1, 44mph top speed calculated) it would be very hard unless you roll backwards down a hill then floor it.
My KZ400 shifter kart (36+HP) wont even pop wheelies, but thats mostly due to the fact that its very hard to get traction haha.
With that gear ratio I doubt you're pulling wheelies without a weird weight setup. I've got a 10/60 setup with a 11hp with a 40s and it just about pops the front wheels off the ground.