The tube you are referring to is the bowl vent that keeps the float chamber at the same pressure is the carburetor air inlet- as the air inlet pressure changes with air filter restriction. Spraying carburetor cleaner in that tube will only raise the liquid level in the bowl. The only way fuel can come out that vent if the float level is set correctly is for the needle valve to be leaking and allowing fuel into the bowl. Did you adjust the float drop to the specified distance? It may be that the float is dropping too far and the needle valve is getting cocked in the valve bore and not shutting off properly. You adjust the drop by bending the vertical tab on the float hinge. The tab touches the needle valve case, or some other part of the carburetor- I don't remember on your 2bbl- and prevents the float from dropping too far. The drop setting is not as critical as the float level, but the float should not go to the bottom of the bowl. There usually is a gauge in the carb kit for measuring the drop distance.

Harvester