If your getting the vito's kit it comes with a jet kit for the stock carb. It includes different needles and main jets. Like 89custom said though, you should really look into a bigger carb for the 240 kit.
You want to know how fast it'll go with the 240 kit. Go out into the road right now and see how fast it goes then add maybe 2-4 mph more. Thats how fast your 240 blaster will go. If you wanna go faster then you'll need to regear your quad. Just because you add more cc's doesn't mean your going to add more speed. It'll just get there quicker, thats all.