Right, as solo says, with slides lifted by cable you don't really need a manometer, and you have two synch. adjustments to make.The throttle stops control synch at idle, and the cable top adjusters control synch off idle. Another way to adjust off-idle synch is by feel. Remove air cleaners, stick finger in intake bell, open the throttle, and feel for the slide. Set adjusters so that slides clear the venturi at the same time. When you have the carb top adjusters set and the throttle stops set well enough to let the motor idle, you can fine tune idle synch by touch (one finger against each slide, feeling to see if they lift at the same time) or by ear (listening for the "click" when slides hit the throttle stops).
You might want to click the Tech button and find the link to the VM section of the XS650 Garage USA Carb Guide. You might save yourself some frustration if you read it before you start tuning.
