Tom,

If/when the seals where the crankshaft exit the engine go bad, the engine cannot develop the pulse that operates the fuel pump. It will also have difficulty drawing the fuel/air mixture into the engine. The engine creates a vacuum at the carb when the piston is on its way up, draws the fuel/air mixture into the crankcase area, and when the piston is on its way down, (after it closes the intake port), it pressurizes this mixture and sends it into the combustion area once the transfer ports open. This is the pulse that operates the fuel pump, and this is how the engine draws the air/fuel mixture into the crankcase and then sends it to the combustion area. If there is a leakage in those seal(s), this whole process cannot occurr properly. This is of course, completely different from four stroke car engines that you might be familiar with, whereby a leaking crank seal only leaks oil, and doesn't affect engine operation. I plug all outlets on a two-stroke engine and use a vacuum/pressure pump and gauge to check crankshaft seals, but they are so easy to replace, that is what I would try in your case. This is of course assuming, that you have no air leaks whatsoever in your fuel tank/supply system.

Good luck,
AV8TOR