This XS 650 is a dual carb bike so it is important to check that both carbs are in synch with each other. Carbs that are out of synch will cause idle and engine performance issues. For this job I made a simple manometer out of a yardstick some fuel line and some automatic transmission fluid.
Note that valve adjustment, carb rebuild, ignition checks, and compression test should be done before synchronizing the carbs. Trying to tune a motor that is tired or mechanically damaged is mostly a waste of time. All engine components need to be in good shape to get a proper tune.
The first thing I do is warm up the bike to normal operating temperature. Next I hook up both ends of the manometer to the plastic nipples on the intake manifolds.
Start the bike and set the idle to spec. Check the reading on the manometer. If the fluid levels are not equal on either side adjust the synch screw on the carb to make the fluid levels as close as possible to each other. You should hear the engine smooth out as the levels get close to each other. Once the levels on the manometer are good adjust the idle speed with the “curb idle” screw back to spec. Shut down the engine and open the throttle a couple of times. Start the bike again to verify the levels in the manometer and idle speed. If all is good unhook the manometer and cap the nipples on the intake manifold.
This is what I started with. See the difference in the fluid levels.
After adjustment. Levels are close to each other.