An example of mis-information again. What the other poster may have been referring to is that the VOES that is on your original configuration needs to remain connected to the manifold to provide for SPARK advance/retard timing. The line from the manifold to the gas tank vacuum petcock should have been plugged if you replaced that petcock with a manual one. If plugged correctly, there will be no affect on the VOES operation.
So, you do not NEED to replace the Keihin CV40 carb on your EVO unless you want to. But I would ask WHY you want to? The CV40 is a great little carb! Very easy to understand and work on. Do some research on here to understand that carb, and you will likely decide to stick with it.
TQ