Had this same problem on my 65.

It would happen after the engine was run for a while (hot), then after it was shut off fuel would leak out the vent hole at the top of the float chamber. In my case it happened on the front carb. Very frustrating (and dangerous).

Fiddled with the float clearance a zillion times, but ended up following the specs. Removed and cleaned the needle valves a zillion times, but to no avail. I had new valves (viton tipped ones, not the grose jets) already installed so I figured that could not be it. Well it was.

I switched the front carb valve with the back carb valve and sure enough, the front carb was fine but now the back carb started leaking out the vent hole. So it was a defective valve.

I removed the valve and replaced it with an old one had in my toolbox. Viola. Fixed. No overflowing. The tops of both float chambers, dry as a bone.

Try switching the needle valves around and if your front carb overflows and your back carb is dry, then it is the valve. Time to clean it or replace it. Probably replace both while you are at it.

waggin

65 220 wagon
85 245 turbo wagon