rebuilt 4.9 will not idle with vacuum line connected
 

We have a rebuilt 4.9 carb motor that will not idle with the vacuum line hooked to the brake booster attached . could the carb be the problem? I will be grateful for any suggestions. Thanks

Generally that indicates that the check valve or diaphragm in the Brake Booster is shot.

Could also indicate that you have the throttle blades or choke closed too far and the engine is struggling to idle when you take away a source of air that it is actively using.

Thank you both. I an thinking carb be cause it runs like a charm when you pull the vacuum line from the booster and it sucks in more air. thanks again