The most important thing to synchronize is the idle adjustment. Back off the idle speed screws until the throttle plates are completely closed - seated in the bores. Turn the speed screws until they just contact the throttle levers. Then make speed adjustments by turning both screws in the same amount.
Be sure the ends of the screws are flat - face them off to true up if necessary.
Two carbs will generally idle richer than either of those carbs used separately, so be prepared to lean down the idle circuits, again turning each screw inward the same amount.
Check your linkage at WOT to be sure both carbs are fully open.
Use two throttle return springs, and you are good to go.
Works for me...
