I meant the carb bowl vent tube, it's in that T at the top of the carb stack and runs under the frame where critters and debris can block it. If it doesn't allow the air to flow freely the gas won't be pushed up the jets once the bowl level starts lowering. A different kind of vacuum problem but it is a possibility.

A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)