I found this thread searching for predator 670 carb tuning tips. Can't believe it didn't come up a long time ago when I was searching for CVTech CVT adjustment info.
I have an American Sportworks Bulldog 300. It's the "300cc" (277cc) version of the same buggy you have, and I also swapped a predator 670 into it. My primary CVT pulley did not have the stoke limiter inside like yours. On mine, the stroke limit was a "feature" of the shaft. I'm curious what year model your buggy is, and why our clutches are different. For my year model I believe the clutches were the same on all the models up to the 650.
In order to free up the primary to spool all the way, I had to put the primary pulley in my lathe and "delete" the stroke limiting "feature." That made a YUGE difference. So I applied the same type of modification to the secondary pulley, allowing it to open up further. Another quite appreciable difference.
Here are a couple of links with pictures of my modifications to the primary pulley...
...and I'll attach some pictures of my modifications to the secondary pulley.
If you have a friend with a lathe you could probably still apply these concepts to your CVT and get even more shift range and speed out of it. I'm getting 41mph on virtually the same buggy as you, same drivetrain, and with my 670 bone stock. On top of that, something is wrong with my carb and I don't get the 4000 rpm as advertised, never have; I get 3800rpm in neutral, wide open Throttle (measured by handheld tach). I'm guessing no more than 3600RPM at max speed. Once I put a better carb on it and get up to 5000 rpm, I should (by the numbers) be able to hit close to 60mph. But i don't have the cojones for that; this thing feels life threatening already any faster than 35mph. I will make some modifications to the suspension and add some disk brakes front and rear, then maybe we can see about 60mph.
How is that mikuni carb treating you? I'm about ready to send this stock china carb off to that fellow in iceland with all the hydraulic presses.