Charcoal - mostly carbon with a little ash from the original material that is used as the base for the charcoal. It makes no sense to worry about less than a quart of the stuff that is mostly carbon and may even get burned in the combustion process.

I believe that the material in the canisters is actually activated charcoal, that's charcoal that has been altered by a heating process that expands the chunks and increases the surface area greatly. In the canister the activated charcoal adsorbs the fuel molecules so they don't escape to the atmosphere. When the engine is running and mets certain conditions, air is drawn through the canister and carries it into the engine's intake tract, and it is burned as part of the regular combustion process.

If you walk through a parking lot on a hot summer day you will notice that very few have a gasoline smell around them. Those that do have had their systems modified or removed, or are old enough that it wasn't required by the EPA. I prefer not having to deal with gasoline vapors except when I want to, therefore I am in favor of evaporative emission controls. They do not affect performance.

You can buy activated charcoal at Walmart in the pet section. I'd suggest that the foam air filter from a late Briggs and Stratton engine would work to keep the charcoal in the canister. Unfortunately most canisters are somewhat hard to get into. Replacements, if you could find one, are usually expensive.

R.