Your problem may actually be compression? You need to use a Automotive compression tester and the compression should be greater than 120# after a dozen flips.

Another problem often overlooked is the skirt of the piston on the intake side if it is one of the piston ported variety. With a lot of piston clearance on the intake side they just will not generate enough crankcase vacuum.

In a old engine the crankshaft seals leak and the engine will be bad about drawing fuel through the carb and on top of the piston.