heres what i have and these work fine.i read somewhere that the number on the intake,under the choke means somthing like the venturi is half that number in mm.dont know if this is true or not.i was told you want at least 11mm venturi.
the numbers im giving you are carb and the number on intake opening.
poulan33cc--carb--wa19---throat 27
ryobi31cc--carb--wa199--throat 18--changing to 20
quadra35cc--wa00--throat28
echo21or22cc--wa199--throat18.--leaving as is.
hope this helps some. i dont look at 100s of numbers.i use a 6.99 steel slide micrometer and measure the results with a ruler that has inches and mm on both sides.