You probably have two places where you can take slack out of the cable. The first is typically right at the throttle housing, and the second is usually on top of the carb. Hopefully, both are covered by rubber boots to keep junk out of the cable when you're not adjusting it!
If you try adjusting the slack at both places and there's still slack, you're probably dealing with the stock-style cable being too long for the non-stock carb.
Motion Pro can make you a custom cable if worse comes to worse.
