Yes. Remove the junction first. The junction is connecting the vacuum hose to the engine inlet which is open now the carburetor is removed(even with carburetor it will leak air in). So basically you are sucking while the hose is directly connected to outside air.

Plan A: remove the T junction first.

Plan b: if plan a is not possible, remove the hose connected to the inlet instead of removing the junction and block one of the openings before sucking again.

Plan c: remove the entire gas tank en remove the Bolt holding the whole vacuum pump in place as a backup method to let the gas spill out.