It's a common occurrence for the top half of a tilly to end up warped over time.
How I fixed mine:
I completely disassembled the carb, taking off everything I possibly could, using C-clamps I seated the top to the bottom half, and then stuck it in the oven, 350-400, for at least an hour, using mits I snugged down the clamps, (don't over tighten) continued heating for another hour.
Turn off oven and let cool completely, in the oven. This is an important step, let it cool slowly, don't rush this part.
As for the float, once you get it back together with the float installed on the top half of the carb, turn the top half so the float is facing up, adjust so as the top of the float is one inch above the flange where the gasket would sit.
Make sure the float is level after you make this adjustment (this is important)
And that's all there is to it, solved my leaky carb problem, hope it helps you.
I'm not 100% on the oven temps, (I am getting up there in age) may want to let some others chime in on that.