Lancia Beta Forum
Technical stuff => Fuel System Carb => Topic started by: JASPER_40 on July 15, 2026, 12:26:53 PM
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I have this mystery item located in the air box which is sits inside the air filter space. What do you think it is for ?
The item has 2 pipe connections beneath the air box which have been capped off on my car. They look like vacuum connections maybe ?
Thinking that it may be something to do with the emmission control system that used to exist for my Australian delivered car which has long since been deleted.
Cheers,
Steve
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It is a sort of vacuum switch for the diaphram that switches over the airbox air intake flap between hot and cold air. No real need for hot air in our warm world car use so a good thing to remove and isolate.
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whole lot is gone from my SA car, interestingly the manifold metalwork has the hose connection blocked off and another SA Beta that was up for sale a few months back had the same. I wonder if its deleted from new?
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It is a sort of vacuum switch for the diaphram that switches over the airbox air intake flap between hot and cold air. No real need for hot air in our warm world car use so a good thing to remove and isolate.
I always thought that twin cams get carb icing at winter temperatures on the motorway? I've definitely experienced it myself in the past.
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"Carb Icing".....alien concept to us Western Australians. ;D
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It is a sort of vacuum switch for the diaphram that switches over the airbox air intake flap between hot and cold air. No real need for hot air in our warm world car use so a good thing to remove and isolate.
Yeah, I reckon this must be right. There is a vacuum take off for the air box diaphragm that works the actual flap but I can't work out how the vacuum switch is plumbed in to the diaphragm unless the vacuum supply first goes through the switch and then onto the diaphragm. The ID of the components are quite different....there may be other components missing ?
Not seen a pic anwhere of how this flap is suppsed to be connected / operated.
It would never be actuated in this climate but might be nice to get it re-commiossioned just for the bragging rights. 8)
Cheers,
Steve
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I'll send you a picture let me look it up. If you only use the car in nice weather it's not an issue but if you drive at low external temperature at constant high speed it can be.
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AI just found this for me ....
How the Pre-Heater Vacuum System Works
The Vacuum Source: A vacuum line connects the intake manifold to a temperature sensor (thermoswitch) located inside the air filter housing.
Cold Engine: When the engine is cold, the sensor is open. This allows vacuum to pass through to a vacuum actuator (servo) mounted on the air cleaner snorkel.
Flap Activation: The vacuum pulls the actuator, closing off cold outside air and opening the flap to pull hot air off the exhaust manifold (via the pre-heater stove pipe).
Warm Engine: As the engine warms up, the sensor detects the increased heat and closes, cutting off the vacuum. A spring then returns the flap to its rest position to pull in cooler, denser outside air.
Modifications: In many warm climates, Betas operate perfectly fine without the pre-heater stove pipe. Some owners permanently remove the pre-heater tube and block the vacuum line to clean up the engine bay, as it is only strictly needed for freezing climates and strict emissions testing.
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Ok so AI also tells me that the way this works is that the vacuum from the base of the carb is connected to the thermoswitch in the air box which is then connected to the flap diaphragm.
Mine were all capped off and I have made the plumbing connections as suggested and now will test it somehow, It will never actuate the flap due to the climate at least it is connected.
Cheers,
Steve