Weber float levels my experience
 

IDA 40 on my 67S
I'm an novice to start with.
All sorts of running issues over the years. Flooding. Smell of petrol. Bad idle
So two sets of new needle and seats. New floats. Carbs on and off 5 times. Done perfectly. To the book. Mixed all the new parts up. Carbs still flood. Use the PMO gauge. All are perfectly the same and too high. Dropped every needle .70mm and they are now perfect. Runs well no flooding. What I'm getting at is by the book settings it would never run. You have to set it to the PMO float gauge.
So my float is 12.5 mm
Tang to base is 18mm
Now rather than 18.5 mm for the needle I now have 19.2 mm
I now have a perfect float height.
I'm amazed how .7mm has fixed my issues. They are very fussy.
Modern fuel ?? Modern parts ??
Don't know but it works
Lyndon