by George Lyle
"This air cleaner has two flaps in its snout. One of the flaps has a weight on it: you know the one that hasn't been ripped off and destroyed on most stock air cleaners--somebody usually has this one wired open."
This flap, for all I know, is there to close off the crankcase blow-by tube when the airflow through the intake is high. The weight normally keeps the flap angled up, which opens the crankcase vent into the air cleaner. My assumption is that this helps to prevent detonation caused by excessive crankcase blow-by. It normally bobs up and down quite a bit at idle, which is probably why folks wire it up.
"Then there's another one, and it has a business on the outside that looks spring loaded. It looks like this spring-loaded thing opens and closes the second flap, choosing between hot intake air and cold."
That's what it does. There is a wax pellet thermostat located inside the filter housing (it's that bullet-shaped thing that you can see from the inside of the housing). This thermostat senses the temperature of the intake air and pushes a rod in and out. This rod varies the position of the flap inside the neck of the air cleaner which controls the mix of the air. [Editor's Note: This describes a '71 air cleaner. On '68-'70 models this flap is controlled via a cable attached to the right side cooling flaps which are actuated by thermostat expansion/contraction].
This is a very nice automatic device. The only problem is that my thermostat is kaput! I haven't even tried to get a replacement, which I doubt is available (anyone get one lately?). I get around the problem with the crude method of installing and removing the hot air duct depending upon the weather. When the weather gets cool the duct is installed. When it warms up the duct is removed and a plug installed in the hot air inlet in the breast tin. Make sure that you plug this hole, as it can be a major hot-air leak! I use a expanding freeze plug to seal it. This method works great for me, and there are quite a few cars that work this way from the factory (albeit with a "winter/summer" lever, rather than removing parts!)
Having hot air going to the carb really improves drivability at low temperatures. Without the hot air the carb tends to stumble and lag when you want to accelerate. With hot air the car performs just like in the summer.
"How does this thing work? I can't figure it out. Is that spring-loaded thing some sort of thermostat? It all seems self-contained. Hmmm. Also there seem to be two places for a hose to the crankcase, where did the one go that doesn't go to the oil fill?"
The inlet under the neck goes to the oil filler. The other inlet (in the side of the "can") goes to the charcoal canister. It is the route by which fuel vapor from the canister finds its way into the air cleaner and hence into the engine. If you don't have a charcoal canister you just plug this hole.
"Could you give me some idea as to the angle the weighted flap should be resting at with the engine stopped?"
On my '71, the weight points toward the snout of the air cleaner, slightly below horizontal. The flap attached to the weight is held up against the top of the intake by the weight. When the engine starts, the vacuum pulls the flap open, which raises the weight to a position above horizontal.
I may have been premature in saying that the purpose of the flap was to shut the crankcase vent tube. Having examined it more closely, I think that the idea is to provide a constant, slight vacuum to the crankcase vent over a wide range of engine speeds and loads.
Mine still works fine, but I'm thinking of some machined brass replacements for the plastic pivots, which are fairly loose.
