If the engine runs smoothly at idle, then theres no problem there. That leaves the most likely culprit the CVT. Having sat for so long, and with the rear wheel turning at idle, it sounds like the variator plates aren't opening/closing like they should. Not a whole lot of parts in that CVT and I seriously doubt any have gone bad; maybe a good cleaning is all that is needed. Might be worth your while to talk to a Honda shop tech to see what they suggest, and get an estimate on cleaning/checking the CVT.