Randall-I came away from the discussion that the spring is used to dampen vibration cause by the engine. It was calculated (FWIW)that 8-10lbs pressure would be needed to fully compress the spring. Someone attached lit. from Burlen on setting float level. It showed an hs carb and spring loaded float needle. The instruction stated that the level be set with just the weight of the float on the needle, not with the spring compressed. I have wondered about which was the correct way to set the float level, but the discussion answered my question.
KVH-The float&needle valve is used to maintain the fuel level in the jet about 1/8"-1/4" from the top. It works exactly like the float assembly in a toilet. If the jet sticks in the open position, fuel will go out the over flow tube and or into the carb throat,sometimes even into the crankcase. If you have used the priming lever on the fuel pump, you will notice that the resistance stops when the float bowls are full because the pressure in the delivery line holds the fuel pump diagragm down against the pressure of the diaphagm spring, preventing it from sucking gas from the tank. That is probably a foggy description, but it is paraphrased from the shop manual.
Berry