Float bowls draining dry when sitting for a while? Sound suspicious for this given that fires right off when warm. What does accelerator pump put out when pumping accelerator when cold? Leave air cleaner off when parking in garage after a run. Can you smell strong fuel odor?

Never owned a Speed Demon carb, have no guesses as to what may be wrong if bowls are running dry except usual gasket or loose fitting inside carb.

Float levels ok?