got a 75 F-100 with a re-built 400 and a 2 bbl re-built carb installed about 1 yr ago. Ran great for the few trips I've taken since getting the carb and then it started overflowing.
When I would take the needle out and re-install (It all looked great, no dirt at all) it would run fine for a while, but everytime I was sure it was good to go...overflow again.
Put a new fuel line on it and an aftermarket in-line fuel filter and it still overflowed.
Went ahead and got a re-build kit and replaced the perfect looking needle/seat and gasket. Thought sure that would do it...drove it about 30 miles and it did fine. Next day I cranked it just for the heck of it and........Yep, overflowed again!!!
What now? Fuel pump??? The pump seems to be fine. No noise, no leaks.
If the float is saturated, it's useless. The instructions in the card kit should have had specs for a wet check, but it's a little tricky and I don't recommend it which is probably why they don't include it any more. Taking the air horn off a Motorcraft 2bbl is easy enough and the engine will idle fine with it off. Keeping the fan from blowing stuff everywhere (including in your clean carb) is another matter.
Save yourself the trouble... spend $8.95 for the float and be done with it.