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ATC Air Cleaner Trouble


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Since it's getting colder out, I wanted to make sure my stock air cleaner is doing what it should. Well, it seems to work ok when I start my truck ('80 720 w/ L20B, stock carb) as the flapper door in the air cleaner closes when the engine is started. However, it seems to stay closed no matter how far or how long I drive. It seems to make it run a little rich. I am assuming that since my flapper door is not stuck or anything that it is ok and that the plastic sensor is at fault. Do these things actually fail?


From what I understand, when the engine is cold, the vacuum passage is open to manifold vacuum. Then, at a certain temperature, it closes off and cuts off manifold vacuum. Is this right? I did a test with a vacuum gauge the other day and after driving enough to thoroughly warm up the engine, I still had 5 hg of vacuum at the hose that connects to the vacuum motor on the air cleaner. The flow was reduced, but not enough to keep the door from closing what looks like too much.


Any quick and dirty test I can do on the sensor? Am I correct in my assumption that the sensor is at fault here? It just doesn't seem to open up enought when it should be wide open..

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