My Dad and I are having a heated discussion about vacuum sync'ing carbs vs. bench sync'ing.
He believes, with all his heart, that you can't get any better than a bench sync; that all butterflies, throttles, slides, etc. are mechanically, physically exact and that anything you do after that will disrupt the equalization.
I believe that vacuum sync'ing will account for differences in the engine from cylinder to cylinder. Low or different compression, valves, etc.
Please educate BOTH of us on which one is better (vacuum... 
) and why. Please provide plenty of evidence, documentation, proof, videos, links, etc. My Dad is very skeptical of information on the internet. He's from the school of thought that "Anyone can put anything on the internet...doesn't mean it's right. I can type in that bench sync'ing is best and vacuum is wrong".
I personally have had very good luck with bench sync'ing. I've had a few bikes that were perfect right off the bat once I put vacuum gauges on them, or so close that it wasn't worth messing with.
I've also seen where all four carbs read differently.
We're currently working on a set of CV carbs. I tried to explain to him that, especially with diaphragm carbs, unlike mechanical slides, that even a bench sync won't make the diaphragms/slides rise uniformly. When I asked him "OK, I bench sync the butterflies and put the gauges on it and one carb/cylinder has 10 inches less vacuum.....what do you do?" HIs reply? "Take off the gauges and throw 'em away."
Help me out here. or, if I'm wrong, say so and explain why.
I'll be cross posting this on several forums to get a wide range of opinions.
I thought that too for a few weeks until I noticed that where the two carbs on the left connect to the two carbs on the right, there is a place where the throttle shafts join together. That is THE problem.
You will notice that when bench syncing them with calipers and getting them spot on that when you connect the vacuum gauges that two of the carbs are still not the same.
That is because of how those throttle shafts are linked together. Look at that closely and you will see why a vacuum sync will get you even better results.
