This might help with places to start looking.
http://www.obd-codes.com/p0440
There is a decent vid on the page that while not a Sporty, most systems share the same basic design (though there could be differences).

Mine throws a P0442 at me from time to time. Most of the time it is just because the guy that pumped my gas (We are not allowed to pump our own on Oregon....) didn't tighten the cap to/past 3 clicks.
Once though it was a plugged up EVAP canister filter (this also causes the fuel to back up in the filler and spray back out at you and kick off the pump, the tank vents while filling through the canister). On the 2001 they put the canister and filter under the rear bumper and it gets all plugged with mud. I need to re-locate it up in the frame above the tank as I do spend a decent amount of time in bumper deep slop.

So far though, when I got the codes I've never had a drivablity problem.... Just reset it, check the gas cap or replace the filter and keep going.
So you may have something else going on. But if you have a code I'd go over the EVAP system to start with, first make sure all the hoses are on tight and not cracking where they plug onto stuff. Then go from there.