Really quick question, identify this component?

[Ride The Snake!]

Hello all, I'm just wondering if someone can quickly identify this component found in the picture on the following link:

http://carphotos.cardomain.com/ride_...0009_large.jpg

What is the round component sitting on top of the rear end of the passenger side valve cover? This is not my motor, but my truck has one too in the same location. Can't figure out what this thing is, but it can be turned by hand and doesn't appear to be threaded into the cover. No vacuum lines or anything attached to it.

[bigblock68]

it looks like a push in breather to me

[JWall]

Originally Posted by bigblock68

it looks like a push in breather to me

X2

[GMCJOE]

x3 With a stock air cleaner setup, there would have been a tube running up to the bottom of it.

[SS Tim]

Maybe a little basic info will help. The pictured item is an aftermarket breather. It allows the engine to vent preventing the seals from seeing intenal engine perssure. On a pretty much any post '67 engine there is a PCV (positive crankcase ventilation) system that combines a breather type inlet, often in the air cleaner and a valve connected to the engine at a vacuum source creating a flow through vacuum. It allows crankcase vapors to be burned by the engine where as a breather like this just lets them out. Often they are put on engine to look like a race car or in the belief that a PCV is somehow and indescribably bad, its not.

[Twiz]

Originally Posted by SS Tim

Maybe a little basic info will help. The pictured item is an aftermarket breather. It allows the engine to vent preventing the seals from seeing intenal engine perssure. On a pretty much any post '67 engine there is a PCV (positive crankcase ventilation) system that combines a breather type inlet, often in the air cleaner and a valve connected to the engine at a vacuum source creating a flow through vacuum. It allows crankcase vapors to be burned by the engine where as a breather like this just lets them out. Often they are put on engine to look like a race car or in the belief that a PCV is somehow and indescribably bad, its not.

Ok, then I have a question. I swapted my stock carb with a Edlebrock 600, and hooked up up a PCV valve the way I was told. What exacly does it do? And I also have that breather because thats what the part store(a very reputable aftermarket parts store that was the only place in town that had everything I needed to replace my carb) recomended I get. I use it more at a cover for oil filling, sence my motor used to have the tube in front of the intake manifold untill I had to replace it with a 4 barrel for the carb.

[SS Tim]

Originally Posted by Twiz

Ok, then I have a question. I swapted my stock carb with a Edlebrock 600, and hooked up up a PCV valve the way I was told. What exacly does it do? And I also have that breather because thats what the part store(a very reputable aftermarket parts store that was the only place in town that had everything I needed to replace my carb) recomended I get. I use it more at a cover for oil filling, sence my motor used to have the tube in front of the intake manifold untill I had to replace it with a 4 barrel for the carb.

If you are making up a system as you did. The engine breather air can and should be pulled from the air cleaner. A fitting is attached to the base plate of almost any style air cleaner that an attached hose runs to a valve cover inlet. Then the PCV valve is attached to the other valve cover to pull vapors out. The PCV valve is then attached to your recommended vacuum source thus completeing the loop. Many people prefer the cleaner look by just putting a breather in one cover and pulling out the other. Or worse just putting a breather in each valve cover. Open breathers also allow vapors to escape at engine shutdown, running to the air cleaner base gives a better chance of capture.

[geezer#99]

If you want to hook a hose from the air cleaner to the breather on the cover use a breather like this.
http://www.holley.com/241-213.asp

[Ride The Snake!]

Okay, so it's a breather. Mine doesn't have a hose connecter coming off it. On the driver side valve cover I do have a PCV valve and the hose goes to the back of my Rochester 2G, down at the throttle body. Is this an acceptable setup? If the breather DID have a hose connecter, it would go to the vacuum connecter at the top of the back of the air horn, just under the air cleaner, right? Since it doesn't, do I need to plug that off on the carb?

[Ride The Snake!]

Also, while I'm on the subject of carb connections, does anyone know what the open port is on the back of some Rochester 2G's at the base of the throttle body? There's an unthreaded port about the diameter of a pencil eraser that goes all the way through the throttle body. The flange gasket I have has a hole for it, and nothing seems to connect to it. Isn't this allowing unmetered air to enter down by the throttle valves?

[geezer#99]

I hate to say it!! THat's right!!
PICS!!!
Pcv hose hooks to a manifold vacuum source.
If the breather had a hose connector it would hook to a fresh air source on the aircleaner.
Not sure on the hole in the back of the carb.
Again pics would help.

[Ride The Snake!]

Yeah, I'm still trying to figure out the pics thing. I went to my profile and tried the whole "upload" pictures thing it has on there, and then it created a URL for them on the 67-72chevy website, but when I pasted that link in my forum post, everyone said the links didn't work. So, I'm confused about how to post images. Seems like it should be a lot more f*cking simple.

[Ride The Snake!]

Originally Posted by geezer#99

I hate to say it!! THat's right!!
PICS!!!
Pcv hose hooks to a manifold vacuum source.
If the breather had a hose connector it would hook to a fresh air source on the aircleaner.
Not sure on the hole in the back of the carb.
Again pics would help.

When you say PCV hooks to a manifold vacuum source, can that also be the backside of the throttle body/plate of some carbs?

I'm asking because I'm still trying to figure out the mystery vacuum leak on my truck. I rebuilt my 2G because I suddenly started experiencing a hissing vacuum leak so bad the truck couldn't hold an idle. This was my first carb rebuild, and after trying two different types of flange gasket, I'm still experiencing a leak so bad the truck won't hold an idle. It's getting plenty of gas (but not flooding), and will at best run for several seconds before it dies. I hear a loud suction sound as the engine stalls out, but no loud hissing prior to that, as I did before the rebuild. If I rev the crap out of the motor I can keep it alive. I don't have a lot of vacuum accessories (not even a brake booster) and I've checked and rechecked the gaskets, tried spraying carb cleaner, etc...no luck locating the source of the leak.

The bottom of the throttle body has some sort of heat exchange passage, and I've tried two different flange gaskets--one which has a cutout to contour to this passage, and one that doesn't. Hasn't made any difference in the idle problem. Checked and rechecked the float level, blasted air through every little carb channel. I'm at a total loss, about ready to replace the carb.

I suppose the throttle valve rod could be worn and thus a source of vacuum leak, but so bad the thing can't even idle??

[geezer#99]

Any large manifold vacuum source is good. Your 2G likely has only one on the back of the carb.
The hole on the throttle body you speak of that goes inside. While it's running stick your finger over it and see if there's vacuum and see if it idles better.
That heat passage is there to warm up and keep warmed up your carb.
I'd bet with some pics we'd see your problem right away!!

[SS Tim]

Post some pictures. This is the short version. Its different for a mobile device, need to search for yourself.

[Ride The Snake!]

Okay, here goes nothing. This is the picture of the bottom of my throttle body. Pardon the childish scrawl...might have to do with the fact that I'm left-handed, but writing with a mouse in my right hand...

EDIT: Yes, I have tried plugging that passage with my thumb, and it made no difference whatsoever. I didn't feel it sucking down on my thumb, and the motor still failed to idle. I should note that I did once get it to run, the first time I tried installing the rebuilt carb. But I had to turn the idle screws all the way out (rich) and the thing raced like hell and got HOT. Way hot, despite the thermostat opening.

[Ride The Snake!]

Here's the view from above. The vacuum attachment below the air cleaner on top of the air horn--to breather?

Port through throttle body shown as well.

[SS Tim]

2G Help

2GV•1955-1971 Rochester 2-Jet Small Bore (1-1/4") carburetor manual
http://www.carbkitsource.com/manuals/carbmanuals/CM022.html

2G•1970-1990 Rochester 2-Jet Large Bore (1 1/2") Carburetor Manual
http://www.carbkitsource.com/manuals/carbmanuals/CM107.html

Carb Information List
http://www.carbkitsource.com/carbs/catalog/ChevroletTruck/index.html

[Ride The Snake!]

I bought the online manual through carbkitsource, actually. The diagrams don't appear to show this thru-passage, nor do they depict the vacuum port coming from the back of the air horn just below the air cleaner. I didn't find any mention of these things in the text either, but I didn't read every paragraph of the manual, so it is possible I missed something.

[SS Tim]

OK lets try working the problem like this. What year and model truck do you have? Engine size and transmission? What is the carb number? Have you verified the application is correct for you engine?

[geezer#99]

The port or hole thru throttle body is manifold vacuum. Needs to be plugged. A tube likely slides in there with a cap on it.
Outlined area is source for manifold vacuum. THe one I spoke about should be at the front of the carb. Or just a channel on your intake.

The other line marked to breather. Was it hooked to your air cleaner or do you mean to the breather on the valve cover.
Now you know how how about a pic of your intake and carb gasket and an overall shot of your carb.

[Ride The Snake!]

Originally Posted by SS Tim

OK lets try working the problem like this. What year and model truck do you have? Engine size and transmission? What is the carb number? Have you verified the application is correct for you engine?

-1970 GMC C1500
-I checked the engine, and it appears to be an over the counter crate motor (no VIN suffix on engine ID code), casting on block identifies it as a 1977-1979 350 cid. The motor has blue paint. The valve covers are bolted at the edges, not the middle. I really don't know much else about this motor, but I assume it is a 2-bolt main.
-haven't identified the head
-stock-looking dual headers
-4-spd manual (3+granny)
-Rochester 2G carb, #7040110
-aftermarket Delco-Remy HEI distributor (which my roommate rebuilt nicely)

According to Haynes, this was a carburetor offered as stock on these trucks, depending on the year.

[Ride The Snake!]

Originally Posted by geezer#99

The port or hole thru throttle body is manifold vacuum. Needs to be plugged. A tube likely slides in there with a cap on it.
Outlined area is source for manifold vacuum. THe one I spoke about should be at the front of the carb. Or just a channel on your intake.

The other line marked to breather. Was it hooked to your air cleaner or do you mean to the breather on the valve cover.
Now you know how how about a pic of your intake and carb gasket and an overall shot of your carb.

I will take a picture tomorrow when I'm near the truck. Right now I'm at work and on the other side of town.

I don't believe that hole was ever plugged (the manifold vacuum as you call it). What would a tube coming from it hook up to in another application?

What do you mean by "the one I spoke about should be at the front of the car, or just a channel on your intake."?

[geezer#99]

Maybe for the vac modulator to the tranny or to the vaccuum pot on the dizzy. The hole might have been plugged off with a piece of lead shot too.

[Ride The Snake!]

Originally Posted by geezer#99

Maybe for the vac modulator to the tranny or to the vaccuum pot on the dizzy. The hole might have been plugged off with a piece of lead shot too.

There is a vacuum port on the front of the carb, just under fuel inlet (fuel inlet sticks out towards the passenger side on this model, not frontwards). The vacuum port is angled diagonally, towards the front passenger-side corner of the truck. It's the one going to the vacuum advance on the dizzy. But the port on the back of the air horn, just beneath the air cleaner--that goes to nothing. If I understand what someone else said in an earlier post here, that would be going to the breather, if it were one with a vacuum connecter. Or maybe it would go to some component of the choke...my choke mechanism is nonexistent. Nothing connects to the choke plate, it just flaps freely and stays open unless I close it by hand...though this never caused problems before. It's always been good starting when cold.