Constrictions in the crankcase ventilation pipes - where are they? Ki

[RuiMeneses (RuiMeneses E-Type S3 OTS 73 XJ6 S3 85)]

Good evening everyone,

UPDATE 29.3: The constrictions are at the end of the metal pipe feeding the carburetors , the hole is relatively large with near 3mm diameter. Thanks to Colin on UK Forum) I added a photo, last one

Related to a previous post of mine, this is the scheme of the US crankcase ventilation I found on the UK site.

I disassembled the pipes connecting the carburetors to the crankcase ventilation. The whole pipe from crankcase to the Strombergs is about 8-9 mm internal diameter, including the Stromberg entry point, just after the butterfly (that surprises me, I never expected to see such a large opening in that part of the carburetor )

On the A bank, the rubber elbow connectors to the carburetors had a 5 mm hole venting the carburetor to the atmosphere (!) . The upper part, to the metal pipe connecting to the other bank and to the crankcase, was blocked by a ball from a bearing (Only on the right side) . Courtesy of a previous owner, as rightly suggested by @MarekH
. Purpose unknown.

I have installed new elbows at the Strombergs entry points, but the engine developed a ´sinusoidal´behaviour when idling, with rpm increasing, then decreasing, the amplitude increases until it then stops. I kind of understand this: increased rpm, more blow-by gases, incrased rpm, then mixture gets leaner , rpm drop, gets richer again and the cycle goes on until in one cycle the mixture is so lean that the engine dies. Will re-check carburetors balance now that the air leak on the rubber elbows in Bank A is gone.

By the way, instead of the elbows I used a 10 mm internal diameter gas pipe and it works fine. If you think SNG sells each elbow for 18 USD . That makes 180 USD / meter of regular gas pipe …

Many thanks

Rui

(before , it had only a very slight sinusoid idling behavior)

Also , this.is how the connection.to the cannister looked like . There is a tiny conical filter that was of course obstructed . You may want to check yous, this will prevent the canister to work as it should and lead to gas smell in the garage .

Up, the restrictors on the pipe connecting to the carburetor rubber elbows.

[Michael_Frank]

I’m not that familiar with the V12, but it looks to me as if the PCV system is very similar to the sixes. With this system, the crankcase gas is deposited in the air cleaner, in front of the carb. Which means that the throttle butterfly controls flow and there is no need for a restriction or valve. That’s different from the typical US system where the crankcase vents into the manifold. With the latter system, you need a PCV valve to prevent the mixture from leaning out when you have high vacuum conditions, ie idling.

So it seems to me that the problem lies somewhere in the carb adjustments, not the vent lines. Another possibility is that the charcoal is saturated, leading to a rich condition.

[RuiMeneses (RuiMeneses E-Type S3 OTS 73 XJ6 S3 85)]

Michael,

Indeed I find no indication of restrictions in the parts diagram. That said there is a feedback/ressonance effect due to the engine ventilation system, maybe it will go away with another carb adjustment setting, I will have to try. So the diagram in the UK site is wrong. The ventilation pipes get in the carb body, just before the butterfly valve, not in the filter box. But air is drawn from the filter box to vent the canister.

The canister circuit plays no role in the mixture , in fact the diameter of the canister ventilation pipe is way smaller that the crankcase vent pipe . In my case it was completely obstructed .

More information here:

https://forum.etypeuk.com/viewtopic.php?f=6&t=17995&p=160484#p160484

Best
Rui

[Michael_Frank]

A couple of thoughts:

1. The gas cap shouldn’t be vented. You may be drawing air through the evap system.

2. The blowby gas will be pretty hot, so maybe the temperature compensators in the carbs have something to do with this.