Some bikes (not all) have issues when the fuel in the gas tank gets low. I think everyones vent in the gas cap functions a little different related to the vacuum it can hold. The weight (head pressure?) of the fuel is not enough to flow gas properly so the bike starves and/or will cut off. I don't believe this has been proved by anyone, but it is a pretty good theory. >>>SNIP<<< It is good insurance for the carbs.
+1 yep, I noticed this right after I installed my first one 9-10 yrs. ago... But for some reason, I haven't noticed it over the past year or two as I routinely run the tank into the reserve zone.... The other downside is that it does slow down the fuel flow to the bowls & I have run into fuel starvation when hammerinmg the bike(let's say 90+
) into a strong headwind!!!