cv carbs are perfect for street use. They make for smooth and even operation with best overall performance. A very well setup VM or direct lift carb will make more power at top end over the cv but are not great for every day 4-stoke street bikes. Members with sohc xs400 bikes that have used both complained about hard engine braking and lots of "jerking" throttle/operation. If your going to race one of these on a track where full on and off throttle happens at every turn, a VM carb setup would be a must. The stock cv carbs are the best setup for stock every day bikes. Yamaha xs400