Suddenly, your bike runs like hell. It's hard to start, idles erratically and feels down on power. What you need is a good sync, a carb sync that is. What's that? On multicylinder bikes with separate carburetors (or fuel-injection throttle bodies), all carbs need to be doing their fair share and operating in tight lockstep with one another. When one or more carburetors gets out of line, some cylinders will be receiving more air and fuel than the others, causing uneven idling and, possibly, surging at cruising speeds.