Finished up a set of carbs for my cb750 K6 project. Set float heights and then did a “Bench Sync”. Been asked what I do, so here it is:
I usually prep a long shank, 1/4 drill bit by making sure the shank is smooth and burr free. I stick it in my drill press backwards and dress the shank with some Emory cloth so it is really smooth and polished.
I start by removing the idle screw/spring and park the spring off to one side. Screw the idle screw in until it touches the operating bridge and add a few turns to the screw. Adjust #2 carb so the slide just barely lifts off the bottom of the carb throat. Lightly lock down the top nut, without moving the base nut/thimble.
Next I crank the idle screw up until I can just slide in the shank end of the 1/4” bit, between the belly of the #2 carb throat and the bottom of the slide. Adjust it so the shank must be flat and centred to just drag in and out. Now using the top adjusters on the other three carbs, set them to the same height….. Lightly lock the top nuts and done. The rubber dust covers on the top adjusters are a pain, but I like the look and they keep the sliding contact faces clean.
Remember to put the spring and washer back in the idle screw! I always check the sync with my old Motion Pro sticks, once the bike is running. I’m often surprised how close this mechanical routine gets it.