Had basically the same problem with a log splitter that had set for over a year without use. It would run only when used "starter fluid". After trying several different things, including changing to a new plug, draining and cleaning out gas tank, etc. None of which got it to running. My brother in law (a small engine mechanic) advised me to take off and clean the carburetor. Which I did and used compressed air to blow out all ports. Back together and it started on the second pull and now runs great. Make sure to use new clean gas and that everything is clean from tank to combustion chamber. If it runs using "starter fluid" its definitely a gas problem.
Regards, Gil