As Frank said, look for a blown headgasket on that model between the cylinders – If bad, compression will be equally low on both cylinders. When you took the carb apart, did you check the thick "donut" gasket that looks like a thick fiber washer, that is at the bottom of the venturi outer housing that hangs down through the hole in the carb float ? If that is bad or missing, you can start it but unless you have the throttle at a slow idle, it will immediately flood and quit in about 2 seconds. Often this falls off when you take the carb apart and you don’t notice it is missing.
Dave