A lot of times the old brass floats have lost their floatyness over time- they get pinhole leaks in the solder joints. I ended up replacing the float in my "B" and it made a huge difference.

Also, I've found that the needle and seat in a lot of carb kits don't seal very well. The reason is that the originals had a chamfer in the seat where the needle rides, and the new ones have a shoulder. I take the old "BB" check ball found in the "B" and a nail-set style punch and use it to stamp a chamfer into the new seat and it makes a huge difference. It gives the needle tip more surface area to seal against and seems to keep it from hanging up.

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A lone amateur built the Ark. A large group of professionals built the Titanic.