[tjs72lemans]

Curious as to how the spring loaded flap doors operate within the air cleaner snorkles? Also, what effect do the vacuum lines have on them? I have the lines hooked to the front carb port that pulls 2 inches vacuum at idle. If I reach into the snorkle and try to manually move the flaps, they don't move. Are they froze?

[AG]

The vacuum diaphragm on the air cleaner should be hooked up to manifold vacuum. Sounds like you have it connected to a ported vacuum source.

[Andretti]

The lines should be teed together and routed to the thermostatic switch in the housing. Then, as AG said, the other line from switch to a manifold vacuum source.
As to how they operate, the system reduces the chance of carburetor icing after starting in cold temperatures. When cold, the thermostatic switch allows manifold vacuum to pass through to the doors, causing them to pull close. When closed, warm air is drawn from the exhaust manifold preheat shroud thru the "stove" pipe and into the carburetor. Meanwhile, the exhaust crossover is heating the intake plenum and warming the air charge. As the vacuum switch gradually reaches its preset temperature it slowly closes off the vacuum, allowing the spring loaded doors to open and cool, unheated air to intake.

[tjs72lemans]

Wow, thanks. There's more to the intake vacuum switch than I thought. I never had it when I rebuilt the motor and thought it was mostly just for emission reasons, so never bothered to find one and put it in. I put a temp gage sending unit there, since I have idiot lights.

[OG68]

You're thinking of the distributor vacuum valve. The one Andretti and AG are talking about is mounted inside the air cleaner. The nipples (2) for the hoses are on the bottom of the air cleaner. Doesn't matter which hose goes on which nipple.

[tjs72lemans]

Ok, so instead of the carb port which pulls 2 inches of vacuum, I should use a manifold port and it will have more vacuum to operate on. Correct? I have all the other lines hooked together as should be. Also, if manifold vacuum can close these doors, shouldn't I be able to move these by hand?

[Held for Ransom]

A '72 intake should have something like this '71 intake has...

[mgarblik]

Originally Posted by tjs72lemans

Ok, so instead of the carb port which pulls 2 inches of vacuum, I should use a manifold port and it will have more vacuum to operate on. Correct? I have all the other lines hooked together as should be. Also, if manifold vacuum can close these doors, shouldn't I be able to move these by hand?

Best way to check the Vacuum actuators, (doors), is to attach each to a hand vacuum pump. If they are good they should close with the pump and hold vacuum. In the real world of modern muscle cars used mostly in warm dry weather, the system doesn't have to work for the car to drive fine. Just make sure the vacuum doors are not stuck in the closed position. That will make it run lousy when the engine warms up.

[tjs72lemans]

Thanks for that pic. When I rebuilt my engine, I put a brass plug in that port, not knowing what it was for. So, that is indeed a vacuum port? I don't want to pull it and have anti freeze rolling out!

[Held for Ransom]

If yours is a stock intake, that's a vacuum source.

[tjs72lemans]

Thank you.