As I mentioned, there is also a good chance that the activated carbon (small charcoal pellets between the two filters) lost quite a bit vapor-storage capacity. This is due to the deactivation of the activated carbon due to permanent saturation of the tiny pores with hydrocarbons. While there are ways to regenerate the activated carbon (Wikipedia link
), it's not very practical at home to heat the canister to high temperatures and flush it with compressed air while the canister is at high temperatures in order to reactivate the carbon.
I haven't done the following but it might be possible to replace the activated-charcoal pellets in the following way:
Removing the cap assembly on the charcoal canister is probably possible. Look at the very first picture in this thread for the schematics of the canister. The cap assembly has the tank and purge valves in it and there is a large center pipe at the bottom of the cap assembly that goes through the top air filter into the activated-carbon pellets. You should be able to pour out the old pellets through that center hole in the filter and replace them with 100%-pure research-grade activated carbon such as this one:Black Magic 100%-Pure Research-Grade Super Activated Carbon by API at Amazon
You would have to put the canister in a vise and turn the cap assembly counterclockwise with a pair of large pliers. You also need to make a new gasket from FEL-PRO sheet gasket material (sold for about $1 per ft in auto stores) when putting the cap assembly back. Again, I haven't done it though and attempt it only if you need to.