carb measuring

[RGP750]

HiAll
I'm rebuilding a 1971 cb125 twin and it should have 18 carbs (not literally) I have got my 20 carbs mixed up with them.
I believe the 18 and 20 is the choke size in MM .
where should I be measuring? is it the width through the inlet?
Cheers Rich

[Johnwebley]

Normally it's the height,

On the CB200 the venturi is narrow, but the full height,

On the 500,the venturi seems circular,

Hope this helps

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[RGP750]

Thanks John I'll take a look at that.