Mysterious vacuum leak

[Machine1964]

I did the old hot rodders trick of spraying carb cleaner on a running motor to listen for idle changes,nothing happened up around the carbs or rubber boots but when I sprayed underneath the vboost manifold (in the actual v of the engine)instantly the rpms dropped and the engine almost died.What could be causing a vacuum leak in underneath the vboost manifold? I sprayed the vboost manifold and nothing happened.Also the motor runs great until it comes up to temp then the motor runs like a dog and the vacuum leak appears.Anyone?:ummm:

 

[MaxMidnight]

The 'what' is easy, the 'where' more difficult.

We could guess at what is causing the issue but the only sure fire way will be to strip and inspect.

If you could try and narrow it down to a particular area that may give you a head start.

 

[johnpclynch]

Could it be cracked rubbers on the vacuum ports, where you plug in for a carb sync?

 

[dannymax]

Could also be the intake manifold o-rings....have you had the carbs & v-boost valve assembly off recently?

 

[[email protected]]

There is a crankcase breather hose that originates down in the valley of the engine and runs up to the underside of the airbox. Maybe the hose is disconnected down low or cracked or something. Not even sure if this would cause the symptom. I guess it could be possible??