I believe its 26mm. There has been some debate over where exactly to measure from, some say the bottom of the carb body,some the gasket surface, some inside the niche the gasket sits in.
I do mine from the bottom of the carb body, to the bottom of the float.
I use a 6" rule with mm listed on one side, and I have bent it 90 degrees to make it a little easier.
The little bridge of metal that holds the 2 floats together needs to be level with the carb body.
Infact, most floats actually have a line or groove on them that you can go by, as in that line on the side of the float should be level
with the bottom of the carb body. Like so, =
It will get you close.
Another thing that makes all of this much easier for me is to take a lenght of tube and put it on the gas inlet for either 1&2 or 3&4
and blow through it. Of course you will need to hold the float that your not working on up, to stop air flow.
When you raise the float up (blow through the tube) and get either the groove on the float or the metal bridge between them, like so = with the bottom of the carb body, it should just stop the air flow at that point.
As far holding them, its a bit of a pain.
I place either the #4 carb or the #1 carb on a towel on the ground and sit indian style with them leaning towards me and to the side so the floats hang open.
When making adjustments, make sure you only bend the tab that contacts the needle.
