Valve Cover Question

[Jason Bourne]

1972 C10 V8

Currently there is an unfilled hole in one of the engine valve covers. See red arrow in the pic.

My question is what should I do with this hole? Does having this open affect performance at all? There is a hose on the other valve cover that connects to the carburetor. I assume this is some type of vacuum advance. I'm thinking the open hole would be causing a vacuum leak but the truck runs ok for the most part.

I am having an issue when the truck warms up, the engine revs drop when sitting at a stop light in drive to the point of the engine almost dying. When the truck is warm the revs increase in Park or Neutral and the engine idles fine.

Maybe there was some type of PCV valve that was there before? I was told the current engine is a 283 that came out of a 1964 Chevy II.

[dmjlambert]

Your arrow is pointing to a device called flame arrestor. It is the fresh air inlet to the engine positive crankcase ventilation (PCV) system. The other valve cover has a PCV valve and hose that sucks blow by gasses into the carburetor and burns it.

The flame arrestor normally has a large hose on it that goes to a spacer between the carburetor and air cleaner, providing fresh filtered air to go into the engine. During heavy engine load especially with a worn engine, blow by gasses may come out of the flame arrestor as well as out of the PCV valve. The cleanest setup is to have a stock air cleaner and spacer with the hose, so all that will get burned as fuel. The flame arrestor keeps flames from a carburetor backfire from going down into the valve cover. You can pull out the flame arrestor and insert a breather, which is a type of air filter, and they usually come in chrome finish from any car parts store.

[dmjlambert]

I doubt the open PCV system with the setup you have is causing your issue with idling and performance. A carburetor usually has 2 idle settings, one is normal idle screw that can be adjusted to give you appropriate idle when the engine is warm, and a fast idle screw that adjusts the idle to a higher speed when the choke is activated. The fast idle adjustment has a little cam that steps down the fast idle to normal idle in about 3 steps as the engine gets up to normal operating temperature and the choke opens more and more. You may notice that when your engine is started from cold, if you let it warm up without touching the gas pedal the idle stays the same and is fast. If you press and release the gas pedal a little after a couple minutes, it may step down to a slower idle. And finally when the engine is warmed up, it steps down to the final normal idle speed.

If you take your air cleaner off and show some pictures of the carburetor, there will be folks who can tell you what kind of carburetor you have and how to adjust the idle on it.

[Jason Bourne]

Originally Posted by dmjlambert

I doubt the open PCV system with the setup you have is causing your issue with idling and performance. A carburetor usually has 2 idle settings, one is normal idle screw that can be adjusted to give you appropriate idle when the engine is warm, and a fast idle screw that adjusts the idle to a higher speed when the choke is activated. The fast idle adjustment has a little cam that steps down the fast idle to normal idle in about 3 steps as the engine gets up to normal operating temperature and the choke opens more and more. You may notice that when your engine is started from cold, if you let it warm up without touching the gas pedal the idle stays the same and is fast. If you press and release the gas pedal a little after a couple minutes, it may step down to a slower idle. And finally when the engine is warmed up, it steps down to the final normal idle speed.

If you take your air cleaner off and show some pictures of the carburetor, there will be folks who can tell you what kind of carburetor you have and how to adjust the idle on it.

Great information in both your reply’s! I’m posting about my sons truck which we both enjoy working on together. The next time he brings his truck I will take some pics of his carb and post.

[geezer#99]

Looks like an edelbrock electric choke carb.
The setting on your choke likely is effecting your changing idle rpm.
He has a potential fire hazard. He needs to move the fuel line closer to the carb over the inside of the valve cover and intake manifold. As the fuel line is now if the fuel line leaks it’ll land right on those headers.

[Already Gone]

In the picture you can see the hose coming from the air cleaner down to the spot you pointed out in your picture. I replaced my engine and used the original QJet on the rebuilt but have a dual snorkel air cleaner I got from Rock Auto now and have the spacer and hose hooked up on the new engine,.

[howzzzit]

Think this is what you have. I do. Looks like you might be missing the air cleaner extension.

https://www.67-72chevytrucks.com/vbo...d.php?t=818909

[HalfBrit]

If you're not replacing the aftermarket air cleaner and not adding the carb spacer (and connecting hose), this push in breather is what you'll find on most valve covers. Just one example in the link, below. Auto Zone, O'Reillys, Advance usually have them on the shelf.
https://www.summitracing.com/parts/pro-141-754

[howzzzit]

Originally Posted by HalfBrit

If you're not replacing the aftermarket air cleaner and not adding the carb spacer (and connecting hose), this push in breather is what you'll find on most valve covers. Just one example in the link, below. Auto Zone, O'Reillys, Advance usually have them on the shelf.
https://www.summitracing.com/parts/pro-141-754

HalfBrit has an answer. They also sell a rubber cap on Summit to just plug it. Don't see the necessity if you're running a pcv valve. Also, I believe the breather cap will become smelly with oil vapors over time. Older cars had that smell about them. Up to you.

[MikeB]

Originally Posted by Already Gone

...have a dual snorkel air cleaner I got from Rock Auto.

Do you remeber the R/A part number, or what car it was for?

[Jason Bourne]

Thanks for everyone’s reply. I think the push in breather will be the way to go.

[dmjlambert]

I recommend don't throw out the flame arrestor, it is not reproduced, and somebody will want to buy/beg that from you someday.

[howzzzit]

Originally Posted by Jason Bourne

1972 C10 V8

Currently there is an unfilled hole in one of the engine valve covers. See red arrow in the pic.

My question is what should I do with this hole? Does having this open affect performance at all? There is a hose on the other valve cover that connects to the carburetor. I assume this is some type of vacuum advance. I'm thinking the open hole would be causing a vacuum leak but the truck runs ok for the most part.

I am having an issue when the truck warms up, the engine revs drop when sitting at a stop light in drive to the point of the engine almost dying. When the truck is warm the revs increase in Park or Neutral and the engine idles fine.




Maybe there was some type of PCV valve that was there before? I was told the current engine is a 283 that came out of a 1964 Chevy II.

https://www.jalopyjournal.com/forum/...-smell.488852/

FYI

[PbFut]

There is a reason why chevy placed that additional breather tube there. Don't plug it, and don't remove the flame arrester. The spacer is a good thing for calming the air flow after the cleaner and before entry to the carb venturi. The vent you are working is open in the air chamber between filter and carb so I do not think it being open to engine bay affects how the engine runs other than letting a lot of dirt into the oil system. I bet a spacer can be found for pretty cheap. Mine still has the 52 year old hose on it.

[71CHEVYSHORTBED402]

Originally Posted by dmjlambert

I recommend don't throw out the flame arrestor, it is not reproduced, and somebody will want to buy/beg that from you someday.

You got that right. Took me so long to find the first one for my BBC, I eventually bought a second one just in principle

[Already Gone]

Originally Posted by MikeB

Do you remeber the R/A part number, or what car it was for?

Yes application was for a 1972 Camaro Z28 with the 350 engine. If that doesn't help I can probably find the Rock Auto invoice in my myriad hundreds of receipts.

Its now Saturday the 27th and was loking for something and came across the invoice for the Air Cleaner andI bought it in April 2017. Couldn't find it on Rock Auto but Googled the Part Number and this came up. Itsgone up in price quite bit. https://www.goodmarkindustries.com/p...1230704sx.aspx

[schovil69]

Another photo for reference,

[howzzzit]

Originally Posted by PbFut

There is a reason why chevy placed that additional breather tube there. Don't plug it, and don't remove the flame arrester. The spacer is a good thing for calming the air flow after the cleaner and before entry to the carb venturi. The vent you are working is open in the air chamber between filter and carb so I do not think it being open to engine bay affects how the engine runs other than letting a lot of dirt into the oil system. I bet a spacer can be found for pretty cheap. Mine still has the 52 year old hose on it.

Whole set up 30 bucks

[Jason Bourne]

Originally Posted by howzzzit

Whole set up 30 bucks

Thanks for this info. I will show it to my son and see if he is interested in this option.

[PbFut]

For that price you could buy the set. Keep the spacer and resell the cleaner and covers for $50.