Re: First time with a kit
The 70cc K-Star is a piston port kit -- it doesn't use reed valves.
The 70cc treats reed kit does use reeds, and there are suggestions on that page to tell you what reeds/intake to use.
If you're getting the non-reed kit, a 15 Bing will work. If you want more power, you can get a bigger carb -- the 19 PHBG is popular, but you're going to have to tune it right. If you don't tune it right, it will run worse than it would with a properly-tuned 15 Bing.