Thank you for your responses - sorry for the delay, I guess I didn't configure to get notification email on reply.
I tried it again last night, hoping for a miracle, but I can sit on the bike, let it idle, then as soon as I twist the throttle it spins down and dies.
So I think the jets (are they called primary jets?) are completely plugged.
@hypophthalmus - thank you, that was absolutely the feedback I was looking for. I don't ride much in the winter anyway, so will pull it apart and clean it up.
So as to root cause, is this indicative of a trashed fuel filter? Or is it more likely that it was corn particles developing in the carb that finally found their way to the wrong place? I only use corn free gas when I store it over the winter. In the summer I use whatever gas is available.
Thank you,