lawn boy 2 cycle m.#4571 , F101 engine

Hi all , hope some of you boys know 2 cycle .?
I have a really nice lawn boy walk behind that will only fire if i squirt fuel into the intake .? It has the plastic carb. and i think the main jet has unscrewed itself down into the carb. bowl over time . Everything else seems ok.
The main jet screws into a plastic tube that submerges into the carb. bowl.
My question is ; does this jet screw back up into the tube until it seats or is there a setting for it ?

Thanks in advance.