I see the term bench sync. but, what's the procedure? what are you syncing up, and to what spec?
-> When they talk about bench synch they mean using a usually round guage to measure the gap between the bottom of the barrel of the carb and the throttle plate. Sometimes there are specs for this gap, and sometimes not. The idea is to make sure all the throttle plates are open exactly the same amount prior to installation so that the actual vacuum sync goes more smoothly.
In automotive in my experience one is taught to look at the relationship between the edge of the throttle plate and the hole in the throttle bore which lets gas in at idle. Sometimes there are pictures in service manuals which tell you what you are looking for. My bike has such a picture but I have no idea whether yours does.
In any case, setting the throttle plates of all the carbs on an engine to the same place in relation to any known fixed point, and knowing what that point means, will go a long way to making vacuum synching a carb a pleasure rather than a pita. If you know how it should look in relation to the idle inlet, so much the better.
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