Vacuum port question
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From: Wake Forest, NC
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From: San Jose, CA
Ok, I see. And maybe mine had one in the front too, but I don't remember anything but my vacuum tree at the rear.
My 302 had a small 3-port manifold screwed into the back of the intake, and from there went mostly to run the other 3-port vacuum valve thingy for the ignition advance. Nothing else to run on that engine, but by '79 you'd have sworn that the entire truck and engine were run off of vacuum hoses!
Paul
My 302 had a small 3-port manifold screwed into the back of the intake, and from there went mostly to run the other 3-port vacuum valve thingy for the ignition advance. Nothing else to run on that engine, but by '79 you'd have sworn that the entire truck and engine were run off of vacuum hoses!
Paul
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Vacuum valve on snorkel
ok. Tested out the snorkel today and the valve doesn’t want to open. On the air cleaner lid, one side is connected to the snorkel nipple. The other is connected to a vacuum tree to the manifold. Even with engine warm, the snorkel valve isn’t opening. I assumed that once the engine reached temp, the bimetallic valve opens.
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any comments on the above post? I'm guessing the VRDV valve is supposed to decrease vacuum and once the bimetallic valve opens, the manifold vacuum is stronger and opens the snorkel valve? I also noted that my air cleaner lid is not sitting flush and sealing on the base, despite having a seal stuffed in the groove. Not sure if a vacuum leak from there would affect the opening of the snorkel valve/flapper.
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From: San Jose, CA
I see that in your case the default position of the flapper thingy is in the closed position. Meaning "closed" against the main cold air intake and open to the hot exhaust side. That does not sound right I don't think. I'll have to go look at mine again.
My memory (feeble as it is sometimes) tells me it should default to open for cold air to enter, while closing off the part that goes to the exhaust manifold. This way if there is a failure of any component it won't choke off the engine and only feed it hot air all the time.
If you have not already, check to see if it's not jammed up physically in the opening and can still move freely.
I think you should feel some resistance as it moves in it's arc, against the spring/diaphragm of the "pot" there on top of the snorkel where the vacuum line attaches at the valve.
Do you have a vacuum pump you can test the mechanism with? Maybe the main pull-off diaphragm has failed?
Paul
paul
My memory (feeble as it is sometimes) tells me it should default to open for cold air to enter, while closing off the part that goes to the exhaust manifold. This way if there is a failure of any component it won't choke off the engine and only feed it hot air all the time.
If you have not already, check to see if it's not jammed up physically in the opening and can still move freely.
I think you should feel some resistance as it moves in it's arc, against the spring/diaphragm of the "pot" there on top of the snorkel where the vacuum line attaches at the valve.
Do you have a vacuum pump you can test the mechanism with? Maybe the main pull-off diaphragm has failed?
Paul
paul
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I see that in your case the default position of the flapper thingy is in the closed position. Meaning "closed" against the main cold air intake and open to the hot exhaust side. That does not sound right I don't think. I'll have to go look at mine again.
My memory (feeble as it is sometimes) tells me it should default to open for cold air to enter, while closing off the part that goes to the exhaust manifold. This way if there is a failure of any component it won't choke off the engine and only feed it hot air all the time.
If you have not already, check to see if it's not jammed up physically in the opening and can still move freely.
I think you should feel some resistance as it moves in it's arc, against the spring/diaphragm of the "pot" there on top of the snorkel where the vacuum line attaches at the valve.
Do you have a vacuum pump you can test the mechanism with? Maybe the main pull-off diaphragm has failed?
Paul
paul
My memory (feeble as it is sometimes) tells me it should default to open for cold air to enter, while closing off the part that goes to the exhaust manifold. This way if there is a failure of any component it won't choke off the engine and only feed it hot air all the time.
If you have not already, check to see if it's not jammed up physically in the opening and can still move freely.
I think you should feel some resistance as it moves in it's arc, against the spring/diaphragm of the "pot" there on top of the snorkel where the vacuum line attaches at the valve.
Do you have a vacuum pump you can test the mechanism with? Maybe the main pull-off diaphragm has failed?
Paul
paul
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