You will need two gauges for making the balance of both cylinders spontaneously.
the rear cylinder vacuum port is behind the right rear cylinder cover, once you remove the cover you will see the vacuum port and a hose connecting it to the fuel valve. use a 3 way connector or AKA a Y connector to hook up one of the vacuum gauge to the vacuum port and still connecting the fuel valve.
front cylinder vacuum port is behind the left front cylinder cover, it will also be connected to a hose which you will have to also connect to the second vacuum gauge via a 3 way connector.
Once the system has been hooked up leaving no hoses open, set the pilot mixture screw to factory setting on the manual, start the bike and let it run till operating temperature... around 5 to 6 min... I would do 10.
read the vacuum gauge, they should be moving in sync, if not then adjust the throttle balance screw between the two carbs to achieve sync.
before doing so make sure you have fresh plugs, fresh air filter and a clean carb. without the above it will be difficult to get a balance engine.