Air cleaner hose and crankcase breather tube

[Zervun]

I did a search but couldn't find the answer.

My 74' has just a 14" aftermarket aircleaner on it which was there when I bought it.

It's cold in Portland right now so I'm interested in putting the stock back on it (he gave me that as well) however I'm missing a few things.

1. Is it ok to just plug the crankcase ventilation tube entry point in the factory air cleaner where it has the small filter? Does it facilitate some function? Right now I just have a breather on the valve cap.

2. Off of the air cleaner is a tube that I believe connected to one of the tubes via a T piece coming from the quadrajet. It is right next to the vacuum tube that goes to the flap and the look like they go into the thermo valve thingy. Where do I connect it back up to?

I'm also trying to find the thermo valve part # for replacement.

 

[diesel4me]

As long as you run a breather in the valve cover on the passenger side,you can remove the bow tie filter and close off the hole in the air cleaner--but the engine will suck in less dust if you leave it factory...(most of the time the reason the bow tie filter gets "moved" is because the engine has excessive blow by and it oils up the air filter & housing--often the bowtie gets plugged right into the valve cover instead,as a crutch to get by )..

The air cleaner "thermac" door has a vacuum operated device that closes it when its cold,there is either a bi-metallic sensor in the air filter housing the hose from it goes too,and that gets vacuum from a small port on the carb--or it may have a thermal vacuum switch in the thermostat housing that controls it...it stays closed until the underhood temp reaches about 100 degrees or so..when it is closed,the air cleaner gets all its air from the "heat stove" thing on the exhaust manifold via that crinkly aluminum tube,to prevent carb icing and improve cold weather driveability...

I had to have that system working on a 305 I had,or the darn thing would frost up the carb badly on cool damp days,ice would form in the venturi and stall it at idle..I also had to rig my exhaust heat riser valve to stay shut when it was below 30 degrees and humid,that helped a lot to prevent that too..

 

[Zervun]

As long as you run a breather in the valve cover on the passenger side,you can remove the bow tie filter and close off the hole in the air cleaner--but the engine will suck in less dust if you leave it factory...(most of the time the reason the bow tie filter gets "moved" is because the engine has excessive blow by and it oils up the air filter & housing--often the bowtie gets plugged right into the valve cover instead,as a crutch to get by )..

The air cleaner "thermac" door has a vacuum operated device that closes it when its cold,there is either a bi-metallic sensor in the air filter housing the hose from it goes too,and that gets vacuum from a small port on the carb--or it may have a thermal vacuum switch in the thermostat housing that controls it...it stays closed until the underhood temp reaches about 100 degrees or so..when it is closed,the air cleaner gets all its air from the "heat stove" thing on the exhaust manifold via that crinkly aluminum tube,to prevent carb icing and improve cold weather driveability...

I had to have that system working on a 305 I had,or the darn thing would frost up the carb badly on cool damp days,ice would form in the venturi and stall it at idle..I also had to rig my exhaust heat riser valve to stay shut when it was below 30 degrees and humid,that helped a lot to prevent that too..

Thanks much - I guess I just need to figure out which port on the Qjet is vacuum to splice into to feed into the thermac

I have the "L" piece tube that goes from the valve cover into the valve cover and I bought a new "bowtie" filter so I'll put that back on.

 

[diesel4me]

The nipple on the carb should be on the same side as the air cleaner sensor is...if you google image search for emission hose routings and or quadrajet carb images,you'll probably find one that will show you just where it goes--its a manifold vacuum source,not ported,it'll have suction at idle..

 

[Zervun]

The nipple on the carb should be on the same side as the air cleaner sensor is...if you google image search for emission hose routings and or quadrajet carb images,you'll probably find one that will show you just where it goes--its a manifold vacuum source,not ported,it'll have suction at idle..

Thanks much the google search for "quadrajet emission hose" turned up exactly what I needed.

 

[diesel4me]

I am not sure if you will be able to find a new thermac sensor for the air cleaner,I looked at Rock Auto's website,no listing...maybe a dealer will still have a listing but I doubt it..but almost all GM's used the same ones in the 70's ,so a junkyard search will likely be your only source..
Those sensors and the vaccuum motor that operates the flap in the air cleaner housing dont go bad that often..I'd make sure yours doesn't work first!.

 

[Zervun]

I am not sure if you will be able to find a new thermac sensor for the air cleaner,I looked at Rock Auto's website,no listing...maybe a dealer will still have a listing but I doubt it..but almost all GM's used the same ones in the 70's ,so a junkyard search will likely be your only source..
Those sensors and the vaccuum motor that operates the flap in the air cleaner housing dont go bad that often..I'd make sure yours doesn't work first!.

I'm going to test it out first - I thought it would be easy to get but I can only find it and Napa and it's a call to even see if I can get it.

I figured it was a cheap part so was just going to buy it but it seems pretty rare.

 

[diesel4me]

If you look on google I bet there is some available--I did a quick search and found a Camaro/Z28 forum that had a post claiming GM still sells them,and had a few part numbers listed--there are millions of used ones in junkyards though,so I wouldn't worry about finding one..just about every GM car & truck used them for a good 15 years during the late 60's to the mid 80's..