Some one is gona mention it so it might as well be me. 210 miles on a tank means nothing. Please find your mpg next time. Becuase your tank should be something like 14 gallons, so that gives you 15 mpg....a pretty bad mpg I might add. Now you more than likely are only putting in 10 gallons of gas in your "tank", which gives you about 21 mpg...big difference...still not good. Please never put miles on a full tank as I'm willing to bet you've never run it dry.
As to your question...it could be a cause to the fuel problem...I do not know what the charcoal canistor does exactly, but I was under the impression that it filtered something (Charchoal or carbon) which could decrease efficiency. Actually just looked it up in one of my engineering books...charcoal canistor is just used for emissions purposes to control hydrocarbons that leak out from your gas tank due to the vent line that releases pressure. Air is passed through the active charchoal in the canistor while the engine is running which can cause irradic A/F ratios; however, they are corrected by the electronics on the car when it passes through a sensor before entering the cylinder. So I dont know that it can affect the car like you say..but I'm sure its possible or at least it could contribute to another problem.