Yep. With 18" tires, you'd have to gear quite low with a clutch. Speed would be dismal.
I have a 6:1 ratio with a centrifugal clutch that goes 30mph. Not to bad acceleration either.
My bad- I meant to state that if it was geared for offroad prowess, speed would suffer.
Here's the pics you request! Let me know if you need more!
http://s212.photobucket.com/albums/cc318/pr0j3ctxb0x/Go%20Kart%20Pics/
A Comet 30 series is only rated up to 8 HP, but could handle about 10HP at a pinch. You will be burning belts a lot faster though
If you read that it handles 15HP, then you are being lied to. They just want to get a sale and be ****ed the person that buys it. I see you have a 11HP engine. You are going to have to bite the bullet and buy a 40 series. Dont buy the 30 series, it will give you too many headaches.