34PICT3 Modification for PCV Feed

[busman78]

Looking for constructive feedback as to how the carb is now set up.

This is a 70 bay with a 1600cc dual port stock engine with a 34PICT3, both valve covers vented with filters, non stock air cleaner.

Over the weekend I installed a fitting to allow for direct feed of crankcase fumes into the intake manifold neck about 1-1/2" below the carb mounting, this adapter accepts a 12mm line which has an orifice of 3mm and now draws crankcase fumes directly from the oil tower. So far so good.

Now to get the engine to idle/run I plugged the hole in the throttle plate, closed the bypass screw and opened the throttle plate via the throttle adjustment screw, adjusted the volume control screw to get the smoothest idle. I do not run the choke at all. Idle jet is a 60 and main is a 150.

Ideas? Possibly something missed?

[keifernet]

[Wildthings]

I would thing a 3mm hole would be too big. You are basically creating a vacuum leak that you must account for somewhere else in the tuning.

[Bookwus]

Hiya bus,

[busman78]

That is the purpose of the 3mm (.120) orifice, which is a 1/2" brass rod drilled through, then placed inline on the hose, it creates a reduced amount of air but creates a draw against the case bringing clean air in at the valve covers then out at the tower. The port I added since my bus is a 70 and does not have the pre-configured 71 manifold. The concept is not new, VW's FI's sucked the fumes into the manifold. It would be hard to suck oil from the bottom of the case all the way up the tower.

Keifernet, mods on the carb, I am not a fan nor expert on the Solex 34PICT3, more of a Weber kind of guy, the few changes I did to the 34/3 do they sound right as to eliminating the bypass and throttle hole and start using the trottle plate adjustment? Any extra air by the 3mm orifice is compensatable through idle mixture and main/AC jets since it is a fixed flow rate.

Here is a picture of this same type of set up on my 78 bay
https://www.thesamba.com/vw/gallery/pix/527585.jpg

[telford dorr]

You're basically engineering a PCV system. As such, I'd recommend researching the theory and inner workings of PCV valves, as they are generally more than just a plain orifice. Because you're going to get oxygen as well as combustion gases through this valve, your idle mixture and run mixture will be affected. I would think you will need a good full range exhaust gas analyzer to do this right (one of the extended range O2 sensor units, at a minimum.) Carb mods are anybody's guess.
Historical aside: the (people's) state of CA mandated this in the early '60s to eliminate crankcase road draft tubes and the retrofit devices didn't work well. I painfully remember (side effect of being old...) having to install one on a '39 Ford flathead.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[keifernet]

[busman78]

What about the little things I did to bypass some of the 34/3 systems?

I plan on putting some kind of baffle with a cooper scrub pad in line or in the tower to capture oil particles so they drip back into the engine.

[keifernet]

What distributor are you using?

I don't know about trying to modify the carb to use the screw on the throttle arm like that... I don't do it that way.

IMHO the carb is designed to mix air and fuel at idle with the throttle plate closed.... now metering the hole in the plate from model to model ( flange # on German carbs) and differenet distributors sure, but to try and use the screw on the throttle arm to do something it was not designed to do ( set the final idle by opening the throttle plate) I have no input on that.

[busman78]

Using an SVDA, First test run was done using the 34/3 as original config, it worked except the idle would not go below 1K, the mods came about as an attempt to circumvent the system. All the items including the plugged plate can be easily reversed.

Pluging the hole was to compensate for the PCV bleed air, basically the two holes are about the same diameter.

[Wildthings]

The system you are installing works well with FI or so I am told, but I don't know about with carbs. The hole in the throttle plate lets air past the throttle plate so that it can be closed further, but this air still goes through the venturis so it creates vacuum and draws fuel. By removing this air from the venturis you may cause a dead spot. What you are doing certainly can be made to work, but might take a bit of tweaking.

The system which I use on my T4 today and used to use a couple of decades ago on my T1 engines is to take air off the fan shroud, filter it, meter it through a small orifice, and then run it into the crankcase. This was enough to keep the watery deposits from forming on the filler cap and in the rocker boxes.

[busman78]

Wildthings, so you were pressurizing the case, did you road dump the left overs?

I will probably reopen the throttle hole, you are right about the little hesitation. Although the only way to eliminate the higher idle was either close it off or close the bypass screw.

[melville]

Your jetting seems on the fat side. My 1679DP is running 55 pilot and 127.5 main, which per LM-1 is getting me stoich at cruise and 13.0-13.2 at full throttle, with Cali lean-meister gas. Are you really getting that much air through your 3mm orifice?
_________________
2000 M Roadster
79 R100RS
78 R100/7
75 R75/6
65 Standard Micro
57 Sedan

[busman78]

Could be, but a quick run down the interstate yesterday, about 15 miles, pulled over and pulled a plug, a little black on the outer rim, but light chocolate milkshake on the electrode.

[Wildthings]

[busdaddy]

[busman78]

I will try that tomorrow evening, had a 73 Olson step van capture my time tonight. Thanks

[busman78]

Wildthings, did you drill a hole in the top of the case toward the front for the air line?

[Wildthings]

[Desertbusman]

After all this, are you accomplishing anything worthwhile or any better than simply running the case breather to the air cleaner and leaving the carb alone?
_________________
71 Superbug
71 Westy