Originally the carb pulsation line was connected to a nipple installed in the crankcase. The modded engines have the pulse line connected to the black insulator block between the carb and the crankcase. If your engine has a line connected to the crankcase you have the older set up that was prone to this problem.

It's an easy fix to do yourself if the nipple is on the crankcase, just remove the nipple from the CC and plug the hole with a 6-32 grub screw and locktite. Next drill and tap the bottom center of the black insulator block and reinstall the nipple there, you'll need a longer piece of tygon tubing to connect the carb to the nipple.

Something else you need to make sure of is that the pulse line is secured to the nipples on the carb and the CC. Tygon will swell when exposed to gas and these connections can leak air in a short time. Use a pair of zip ties to anchor the tubing to the fittings and to insure a positive seal.