As Mike said, if you do not have a primer bulb in this line or a check valve, you must plug the line and not use it. It will suck air and mess up your mixture if you don't.

The line is actually a air eleminator return device when used in conjunction with a little bulb pump will purge the air out of the carb mechanism at start up. But the engine will run fine if you plug the line up. You just have to make sure you jiggle the crank enough to prime the engine well to make it easier to start.

Or choke it

Enjoy,

Jim