Have you tried to blow thru the carb, maybe it is gummed up as well. If so the engine will not run at all. Also the muffler pressure tap may be plugged. If it is plugged it will be a bear to start and keep running.

Try putting a little fuel into the engine thru the carb, then apply glow heat and then electric starter, If there is no glimmer of a start, check the glow plug and make sure it is glowing bright orange. Even with a stuck ring, it should still start and run if it has fuel ect.

Good Luck

Richard