carb size queery

[thescoot]

New to the forum so heres my first question for all you experts. As I recall, a 1973 cb750 was fitted as standard with 28mm carbs. When I measure mine there 30.5mm at the head side of the throat. Am I measuring the wrong place or have they been changed or modified. They look standard but I think every other part of the motor has been played with which is making me wonder. Any advice will be greatly appreciated.

[K2-K6]

Think they are an "effective" 28mm at the venturi and also not uniformly round on many carbs. Most likely they are std but being measured in different places to where Honda's spec applies.

I've seen them bored to increase this slightly quite a few years ago, remote possibility that you have some that are modded.  Maybe some pictures to compare would give you better indication.