I have had success syncing up my carbs using flathead bits. I'm sure your saying “obviously” but I'll try to explain because I would like input on why I'm delusional. If you have worked on these then you know that the sync screws ( 3 of them ) go thru a plate, thru a spring and die into a plate below. The spring is compressed between these two plates and as you turn the screw left, the spring will decompress. Now what I did. After turning all three screws tight as they will go, I twisted my throttle and observed all three springs (now facing up from twisting the throttle). I seen that spring 3 and 4 had both compressed more than 1 and as a result the gap in-between the top and bottom plates were inconsistent even when tightened to max throughout. Maybe I'm crazy but a lightbulb turned on. Using my smallest flathead bit, I twisted the throttle again and used the width of my flathead to adjust all the gaps according to it (the flathead). It worked. For the first time I rode a bike I bought in boxes.
