Made one of those carb sync tools. They tell you how to sync round slide carbs. They said flatslids sync differant but dont tell you how. Looking for help.They show the tool in the carb section under carb sync

i just use 2 drill bits the same size. seems to work ok

As tunedbyear said, take two drill bits the same size and set them under the slides. adjust the throttle up or down depending on the drill size. Both should fit under each slide the same. If they dont, you will have to open the top of the carb to adjust the slide. If I remember right, there is a nut with a bolt on the shaft that you adjust with.
Thats it. Reset your idle and they shoul be in sync.

try to find a drill bit around 90 thousdaths

90 thousandths amen

ideally the carbs should be synched on how much vacuum they draw both with fuel mixture and carb opening the mixture part to adjust for differences in fuel flow, cylindert effeciency etc, ... I just use the dam drillbits..I saw somebody use the mercury syncer once, it was pretty stressfull.