That is the way to test for air in the fuel line. Did you rebuild the VST and a new diaphragm in the VST air pump? Does pushing the key in still keep it running? Ask the shop to check for voltage at the primer solenoid, motor not running, key in the on position. You should not have any, if any voltage present, bad ignition switch. This causes the primer to inject some fuel, depending on the amount of voltage. The motor would smoke and die out at idle. We didn't try that. In your picture's, are those black gaskets on the carb bowls?