Can you post the make and model of the engine? Sounds like the carburetor needs to be disassembled and thoroughly cleaned.

Note: Besides the carburetor cleaning, also check the breather hole in the gas cap! Also, remove the flywheel cover and check under there for dirt, etc, or a spark plug wire that may have no insulation on it, due to mouse chewing. Clean the rust off the coil legs, and the flywheel magnets, too. Reset the coil to flywheel gap, using a regular business card as a gap setter!
Check for a deteriorated fuel line, as those old rubber lines get soft, and then break apart internally, clogging the carb. Thoroughly clean out the gas tank.

"I have rebuilt the carb. and it still only runs on starting fluid"
"It also will run if I cover then uncover the intake."

All this says fuel starvation, either still plugged carb main jet circuit OR badly leaking intake manifold to engine gasket, cracked Intake Manifold?.

By the way, you do not want to continue to run that engine on starting fluid, use gasoline in a squirt can instead.

Walt Conner