What are the first few things to check?

Is there an automatic choke that isn't working. Is the manual choke
working?
Is the carb letting the fuel drain out when it sits overnight or longer?
Can you fill up the carb with the fuel-line primer bulb? does it get hard
to squeeze after a couple of pumps?

You could get some of that starting fluid to see if that would get it to
fire up sooner. If it won't fire up with starting fluid, then there might
be another problem.