I'll add a strange experience with overflow hoses. I had a '77 Honda 750 motorcycle that ran poorly at over 50mph. A real puzzle - RPM made no difference. The only coincidental factor was road speed. A genius mechanic found the problem to be the carburetor bowl overflow tubes. All four were bundled together with the drain end of the tubes fastened to the frame in front of the rear wheel. The partial vacuum in the frame's slip stream at 55mph caused enough vacuum to suck fuel from the bowls, starving the carbs. And it was all my fault for obsessing over venting - I'm the idiot who modified the drains.
So, if you add a vent to your tank, be sure it terminates into a neutral or positive air space.