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Old 11-26-2021, 08:31 PM
tjs72lemans tjs72lemans is offline
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Default Dual snorkel air cleaner function

When do the flapper doors inside the snorkels close shut? I assumed when cold they closed. Does the vacuum when engine fired up cause them to close when it's cold out? Then open as engine warms?

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Old 11-26-2021, 09:11 PM
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In 71 and 72 Ram Air... Basically there was only Dual air intake working
when Engine is at temp, and WOT giving no vacuum to the vac motor on the ds.
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Old 11-27-2021, 12:19 PM
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I'm not talking about ram air with outside function. Just a normal dual snorkel air cleaner.

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Old 11-27-2021, 12:34 PM
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Basically, they are closed when cold / open when hot. Manifold vacuum is supplied to a thermal sensor located inside the air cleaner assembly, which then feeds the two vacuum motors on the snorkels. As the engine warms up, the sensor opens to allow manifold vacuum to actuate the flaps inside the snorkels.

The picture shows a single, snorkel. The dual snorkel unit simply has a tee in the feed line so that both are actuated at the same time.
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Old 11-27-2021, 07:53 PM
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Quote:
Originally Posted by tjs72lemans View Post
I'm not talking about ram air with outside function. Just a normal dual snorkel air cleaner.
You didnt mention 400 or 455 either.
455 will have 2 Heat risers, and 400's only have 1.
On a 400 The therm motor still works on the side where there isnt a heat riser, but only used to shut off that snorkel when cold.

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Old 11-28-2021, 04:31 PM
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It's a 400 (1972) with only one heat riser. The flaps are both open and it's 40 degrees and car off. I can reach in and move them by hand, so they're not froze or sticky. Why would they not be closed at that temp?

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Old 11-28-2021, 05:17 PM
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Quote:
Originally Posted by tjs72lemans View Post
It's a 400 (1972) with only one heat riser. The flaps are both open and it's 40 degrees and car off. I can reach in and move them by hand, so they're not froze or sticky. Why would they not be closed at that temp?
They need vacuum to close. No vacuum, engine off, the doors are spring loaded open.

Clay

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Old 11-28-2021, 06:35 PM
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Originally Posted by tjs72lemans View Post
It's a 400 (1972) with only one heat riser. The flaps are both open and it's 40 degrees and car off. I can reach in and move them by hand, so they're not froze or sticky. Why would they not be closed at that temp?
The vacuum diaphragm might be junk. Attach a vacuum hose to it and pull vacuum to check it.

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Old 11-29-2021, 09:50 AM
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Thanks. Those are the answers I was looking for.
One more thing. I put ARP bolts in during rebuild. So, now I have no stud sticking up for a stove warmer and pipe to air cleaner. Will this allow the flaps to stay closed when engine warms due to no heat rising?

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Old 11-29-2021, 04:07 PM
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Quote:
Originally Posted by tjs72lemans View Post
Thanks. Those are the answers I was looking for.
One more thing. I put ARP bolts in during rebuild. So, now I have no stud sticking up for a stove warmer and pipe to air cleaner. Will this allow the flaps to stay closed when engine warms due to no heat rising?
Inside the air cleaner is a thermal switch. The vacuum is routed through it first, then to the " flappers".
The warm up time and air coming through the snorkels
Will be delayed if the air is cooler. Still you'll get plenty from
Under the bottom of the snorkel with the open flap where heat tube would be hooked up.
You can eliminate the temp switch . Make sure your choke is working well.

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Old 11-29-2021, 06:07 PM
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Today it was 48 degrees and sunny out in MN. No snow or therefore salt, so I fired up my 55 Chev and went for a ride. Came home and looked at the Pontiac air cleaner and flaps in snorkel open. Fired it up and they stayed open. Went for a ride as an end of year bonus. So, I assume it may be a bad thermal sensor. Or, could both vacuum diaphragms be bad?

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Old 11-30-2021, 02:00 AM
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The old diaphragms I've come across ... more work than don't. Super easy to test with a hand vacuum pump. So either a bad thermal sensor or a crack in a vacuum line. This system uses vacuum ports with a very small orifice to delay open and close speed so they are not flapping open and closed or chattering with changes in vacuum ... easy for the little pin holes to get plugged.
A vacuum leak down stream of the sensor really doesn't show up in the way the engine runs because the orifices are so small. I've seen the lines crack at the sensor fittings a lot.

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Old 11-30-2021, 12:09 PM
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I did put new rubber lines on all connections when I restored this last year. I'll have to see if I can get a hand vacuum pump from someone to check the diaphragms.

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Old 11-30-2021, 01:40 PM
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By the way, if you have to replace them, it can be done. Couple of spot welds to drill out, and tack back, and some repainting would be necessary

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Old 11-30-2021, 01:43 PM
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Quote:
Originally Posted by tjs72lemans View Post
I'll have to see if I can get a hand vacuum pump from someone to check the diaphragms.
I used my mouth for years before buying a mighty-vac. When it wore out I went back to using my mouth.

Clay

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Old 12-01-2021, 12:26 PM
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MMMM, if that's enough to move the flap, it's worth trying. Quick too!
Not sure if I want to ruin the finish I put on my dual snorkel restoring it. Since I drive it mostly when it's fairly warm out, maybe I shouldn't worry about if these flaps close in cold weather. Let them stay open?

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Old 12-01-2021, 02:18 PM
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If your choke works and you have no vacuum leaks, just leave it.. Should be just fine.

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Old 12-01-2021, 03:28 PM
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There is a reason they fail to the open position rather than closed They probably knew when they designed them that six years down the road half of them wouldn't work and would never get fixed.

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Old 12-01-2021, 06:32 PM
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Ya, my choke works good and Cliff's rebuild works awesome.

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