You want to make sure that the butterflys are opening up together for obvious reasons. The only way to check is with a vacuum gauge or manometer. I hook up my vacuum gauges to the engine, run it at 1500 rpm and see if there is a difference in readings. If there is I adjust the adjustment screw situated between the carbs until the vacuum is the same. Hard to see the screw. Once I do that, I adjust the mixture screws (one in each carb) until the engine idles it's best. I then check the balance and readjust if necessary.
If the balance is out a lot, this will smooth out engine vibrations around 3500, cause a subtle increase in power and balance the load equally between 2 cylinders instead of unequally between the 2.
This is the
Carb Balancer I purchased. Got mine for $40 US last year.
