Intake manifold hole 250C open or plugged?

After all this time and all these posts I have found that the tube in the intake manifold of my M130V has been plugged. This is the tube that goes from the center of the manifold to the air cleaner/water seperator for the EGR system. Well, the plug rotted away and now the car runs ALOT different. Is this thing supposed to be open when you tune the carbs??? And then reconnected when you put the air cleaner back on??? Does this explain why I am not getting an even air/fuel mixture after hours and days (and some nights) of trying to get this right, or just more wishful thinking?
Thanks,

[ctaylor738]

I don't know if this is correct or not, but I have always done the carbs with the air cleaner off and the vacuum open. I do not recall any instructions to plug it before adjusting.

You should definitely try a re-adjustment with the system functioning.

Chuck

I thought it should probably be open, because that is the way it would be normally if you take the air cleaner off. I stuck a piece of hose on there with a partial plug for the time being, and even though it stalls now, there is much more power with less rocker knock.
Thanks,

[cth350]

EGR system? Did you mean to say PCV (positive crank case ventilation)?

There is supposed to be a restriction in there. It should not be that great a vacuum loss. Feel free to cap it at the expense of leaking noxious, polluting vapors to the atmosphere.

-CTH

Yes, I mean Positive Crankcase Ventilation, not EGR. Sorry. If the system is completely hooked up, where is the restriction? Is it restricted with the air cleaner off when adjusting the carbs? I am assuming that the water seperator in the air cleaner housing contains some sort of breather element, which is not present on my car. Can't seem to find any specs though.

[cth350]

The system starts with the flame arrestor in the opening of the rocker cover. Lovely name that. Everything is open to the atmosphere from there (no filter either). This is unlike your modern cars that have a small spring loaded valve and a small filter element to trap the junk.

The small tube at the base of the manifold should have a brass plug in it. That plug has a small hole built in to restrict airflow.

-CTH

There is a brass fitting on the bottom of the air cleaner, but the tube just had a bolt in it. When you remove the air cleaner to expose the carbs, what is the tube supposed to look like? Mine is just a peice of fuel hose. It used to just have a bolt in it, but I took it out. I have a flame arrestor!

[cth350]

- Flame arrestor in valve cover to
- right angle hose over air cleaner to
- BIG round air cleaner cover to
- BIG round air cleaner bottom to
- 50mm (or so) oil-proof gas line to
- fitting dead center of intake manifold (which has a brass restrictor in it).

-CTH

[DANTRCAV]

Chris:

Yep, the brass orifice is actually a calculated opening and acts as a metering device to pull liquid particles back into the intake system. Since it is metered the amount of air bypassing the carburation system is calculated into the carb specs. IN THEORY, then, if this hole is plugged the carbs would then be rich in the idle mode (manifold vacuum is higher at lower engine speeds). If you pull the plug out of the manifold (it is a press-fit) with the engine running the engine will die.

I don't know if in the final analysis having the hold plugged or open really makes any difference. When I had the stock Zeniths on my 250C I left it open and connected it to the air cleaner via a short piece of fuel line. The PO had plugged it with a bolt. Can't say I remember any difference. When I put the Webbers on I plugged the hole since I also added K&N air filters and didn't have a good method to connect it. The idle jets were adjusted to match the car anyhow so in my case it now really doesn't matter.

I believe that the actual separator and connecting part(s) might still be available from the dealer - at least I had heard that stated by a local Benz mech.

My .02.

Dan