Vacuum Leak???

[AuroraGirl]

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this last photo is of my oldsmobile 260. the distributor cap has a retainer that holds the plug wires. you can buy them new or i could sell an old ass one.
They are helpful. help assure best contact on the towers

and I pointed out a couple things I saw problematic, feel free to ask questions. if i put an arrow and a ? it was me unsure if its an issue or not but it looks suspicious

 

[AuroraGirl]

on the return spring and throttle cable, your TV cable it appears to be, to me at least, is present on a vehicle with either an updated dipstick from 89-91 or so when they updated them to have a seal at the top and be plastic, but it makes me wonder if you have a 700r4 or a th350. if th350, is a tv cable able to behave like a kickdown cable?

your vacuum block of hardlines is generally ok but is it thread sealed

also, your distributor. idk what a properly timed distributor points at but mine has the connector almost perpendicular with the engine when i timed it by feel because it used to be way the other way, you have a cam tho too, so Just me saying "check that"
your wires are pulled tight, touch, and that can cause insulation issues or them to arc out or weak spark etc. is your distribuutor recurved for cam

 

[Rusty Nail]

Oh wow lol this pic makes it look way different!

But dude.
You have a PCV AND a breather on the same valve cover. Huge problem.
You will have to start by plugging THAT hole, in the valve cover?
The PCV valve relies on engine vacuum to function but since you also have that breather installed, the PCV is effectively negated and de-balled and the carburetor needs that vapor, man!

 

[AuroraGirl]

Oh wow lol this pic makes it look way different!

But dude.
You have a PCV AND a breather on the same valve cover. Huge problem.
You will have to start by plugging THAT hole, in the valve cover?
The PCV valve relies on engine vacuum to function but since you also have that breather installed, the PCV is effectively negated and de-balled and the carburetor needs that vapor, man!

I know my setup isnt perfect but i already know what my problems in these pics are I just have delegated the fixing of them to future me but this is what rusty meant by the PCV thing. one cover needs the valve, preferably your passenger if yours hooks up to the.. side?? Just to be shorter length. dont want to collapse any hose or just have it shorter for simple sake

Then the breather can be on the opposite corner, where the pcv is on his. then the back breather needs to **** and then... idk what would go there to block it up. oil cap? I dont know vortec covers well

 

[born2Run83]

Oh wow lol this pic makes it look way different!

But dude.
You have a PCV AND a breather on the same valve cover. Huge problem.
You will have to start by plugging THAT hole, in the valve cover?
The PCV valve relies on engine vacuum to function but since you also have that breather installed, the PCV is effectively negated and de-balled and the carburetor needs that vapor, man!

I’ve seen sealer type caps for closing off unneeded valve cover holes on top. I’ll get one of these and remove the breather on the driver side. Thank you!

 

[born2Run83]

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this last photo is of my oldsmobile 260. the distributor cap has a retainer that holds the plug wires. you can buy them new or i could sell an old ass one.
They are helpful. help assure best contact on the towers

and I pointed out a couple things I saw problematic, feel free to ask questions. if i put an arrow and a ? it was me unsure if its an issue or not but it looks suspicious

The transmission is a TH350- confirmed vis the pan shape.
The 3/8” line on the psgr side is the vacuum line that routes across the front of the carb to the pcv valve which is on the driver side.
The kick down cable seems to be pulling when I punch it while going down the road at cruise speed.
If that is a leak at the front of the carb it is old. I’ll wipe it off and monitor
The hard block for vacuum lines at the rear of the intake looks to be sealed threaded. I sprayed started fluid around again today and didn’t seem to have any leaks in that area.
RustyNail did bring up a good point on the breather and pcv both on one side with breather on the other cable cover as well.
The cam is mild and the previous owner is unsure of the duration, lift etc, but it does idle pretty lopey. The recent tune I had done did help the acceleration and mid range so what I believe may have happened was with him doing that with the Wideband, he tweaked timing some also.. could this have more or less enhanced the already existing vacuum leaks bc it’s a little more advanced now? The issue was there somewhat prior to taking it to get the AF mixture tuned but was more noticeable when at a stop light, in drive, with brake applied, or in reverse- but in Park it would idle fine.
I’ll seal off the cable cover breather on the PCV (driver side) tomorrow.
I haven’t messed with the choke at all yet. I do notice though when the truck is warm started, it doesn’t fire right up- if I don’t pump the gas a couple times it’ll not fire up- so that prob is choke related

 

[75gmck25]

Every original GM valve cover I’ve seen with two holes is designed so one fits an oil filler cap and the other is for a PCV grommet. The one for the PCV should have visible baffle under it (often just a flat metal plate with an open slit across the middle), while the oil cap hole is usually open and you can see the valve train.

 

[born2Run83]

Every original GM valve cover I’ve seen with two holes is designed so one fits an oil filler cap and the other is for a PCV grommet. The one for the PCV should have visible baffle under it (often just a flat metal plate with an open slit across the middle), while the oil cap hole is usually open and you can see the valve train.

In this case then they had the pcv valve and breather switched. On the psgr side there’s currently a breather, with a baffle plate right under it- and below the pcv on the driver side is exposure to the rocker arms.

 

[Rusty Nail]

Pcv valve gets the baffle yeah... There was a thread awhile back about that very topic breather/pcv/which valve cover but I wasn't gonna say anything.

Maybe itll come up in the search?

 

[born2Run83]

Pcv valve gets the baffle yeah... There was a thread awhile back about that very topic breather/pcv/which valve cover but I wasn't gonna say anything.

Maybe itll come up in the search?

I was able to find that thread in the search and read up on it. Thank you for sharing. It looks like that culprit came down to the Edelbrock intake gaskets. That’s an interesting reason but I have the Performer intake installed on this 350- not sure which gaskets they used to install. I pulled the breathers on both valve covers, one was installed over the baffle plate, and the PCV valve was not over a Baffle. I’m pretty sure there’s a rubber type plug available to close off one of the ports on the valve cover that has both the PCV valve and breather. That may help with the vacuum so I will do that next and also install a vacuum gauge to see where it is during idle.

 

[Camar068]

When i had the 350 installed, I eventually mounted a 1.5" vacuum gauge in the area of the carb. Made it easier to adjust the carb and was a great help down the road troubleshooting the engine. Just a quick glance and you could tell if you had a leak or something else going on.

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[born2Run83]

When i had the 350 installed, I eventually mounted a 1.5" vacuum gauge in the area of the carb. Made it easier to adjust the carb and was a great help down the road troubleshooting the engine. Just a quick glance and you could tell if you had a leak or something else going on.

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Thank you for adding this vacuum page. I’ll hook up to the engine and use this to see where the readings are.

 

[born2Run83]

Update: the photo with two breathers is before.
I removed driver side breather and installed oil cap (push in type) and replaced breather on psgr side. Also installed new pcv valve.
Idle still rough and dies almost instantly.

 

[AuroraGirl]

Update: the photo with two breathers is before.
I removed driver side breather and installed oil cap (push in type) and replaced breather on psgr side. Also installed new pcv valve.
Idle still rough and dies almost instantly.

go back and look at the things i highlighted, because I still see more than one issue but im not repeating myself lol. also read what rusty said.

 

[born2Run83]

Sorry for the late reply here. After running vacuum checks and with the gauge and finding a leak near the rear part of the carb gasket, I changed that out and also with the cam having such a lope to the idle, I barely moved the idle mixture screw clockwise. Problem solved!
Thank you all for the help here. Thankfully it was an extreme issue