Sounds like the typical Briggs V-twin problem.
If so, the main jets belong in the bottom of the emulsion tube, which is the white plastic
tube in the center of the underside of the carb body.
The jets are usually held in place by friction of O-rings on the jets.
These shrink mostly due to ethanol in the gasoline.
The bowl fitting will keep them in place while assembled, but they fall out after bowl removal and uprighting the carb.
Caution--the jets are different sizes!
See here for the discussion as to which goes where:
http://www.lawnmowerforum.com/showthread.php/40652-2-Briggs-V-Twin-questions?highlight=main+jets
See post #55 for the definitive orientation of the 2 jets.
btw--O-rings are available from McMaster Carr, cat# 9262K101
https://www.mcmaster.com/#9262k101/=190aof3
or possibly auto parts store or hydraulic supplier
You can re-install the jets without new O-rings.
Just make sure to put the bowl back on before turning the carb upside right!
Roll Tide Roll!
Good luck!
