Here's my homemade apparatus for setting the throttles to open at the same time. I use it when I can't be bothered getting the manometer out or as an initial setting before using the manometer.
"Borrow" a pair of your wife's finest Knitting needles, thinner and lighter the better. Cut a pair of short rubber tubes about 3/16" id and pierce one end with the needles. Push the tubes onto the exposed inside end of the Carb throttle shaft. With the right tube they hold in place quite firmly.
With the needles arranged either side of the tank you can observe that the throttles open at the same time. The 16" long needles amplify the slightest rotation of the throttle shaft so it's a very sensitive method of mechanically balancing the Carbs.
Being a sad old thing I calculated that 1 degree of rotation results in over 1/4" of movement at the needle tip. In practice you can observe a much smaller movement than this, say 1/10th of a degree or approx .002" at the edge of the throttle disc.
....and if your not into Knitting Lou I find that my 3/16" id manometer tube is a good tight fit on flat top vacuum take off points.
