[clone5]

...never heard of floats becoming heavier....It they did, it could only happen by build up, which would be rather insignificant. Even if real, which I doubt, you could simply drop the level to compensate.

My question;.................... do you really know where the level is????

If floats no longer float due to plastic degradation they can fill with fuel and become "heavier"

 

[clone5]

Overflowing carbs mean that the fuel is not being shut off
This is mainly because of the float valves not seating correctly due to age, wear or debris. Or all of the above
Grab yourself a new set of float valves and ensure the seats are clean and smooth prior to install.

Google "zr7 float valves" to see the part I'm referring to