Carbs and Crankcase Ventilation

[wjdunn3]

My 73 2.0 has dell 40's on it right now and probably will for at least another year. My question is concerning crankcase ventilation. What is the proper configuration with carbs?
Each Cyl hd has a vent port on it. There is also what looks like a vent at the oil filler that contains some type of PCV valve in it (built into the filler box that snaps onto the top of the block). Previous onwner had all three tied into one small (1/4") hose that was run out the back of the car, vebting to atmosphere. However, I appear to have a lot of crankcase pressure (connot hardly pour oil into filler neck with car running without it trying to spit half back out. Is this due to the venting config or is something else wrong?

[John Rogers]

That little plastic thingy is the PCV valve. Should be clean and free to move. The gasket on the bottom of the oil filler assembly should be a good seal and you might have to bend the wire bale to get it to fit tight. On both of our Porsches, the vents go to the air cleaner, downstream of the filter so there is a slight vacuum effect and the fumes are then burned. The pressure at the filler can be caused by blow-by and insufficient crankcase venting. Try larger, separate hoses and crankcase pressure should go down.

[JP Noonan]

K+N makes little round breathers that snap into the vavles covers on domestic cars. It allows the vapor to vent to the outside (polluting the air) but doesn't let dirt back in.

On FI systems there is a very important "flashback valve". It is a t-fitting from the heads then to the air distributor. Inside the flashback valve is a fine wire screen, this keeps a backfire in the intake from igniting the oil vapor in the case. If this were to happen the case can completely blow apart. With that said, my old 32/36 carb had a fitting on the bottom of the air filter housing which was hooked up to the PCV on my 1.8L and the case never blew up.

If you still have the flashback vavle (it is mounted to the bar that controls the cooling flaps, on the fan houseing) I would use it.

[Dave at Pelican Parts]

The common things to do are to either run the combined vent hose to a catch-bottle (illegal just about everywhere, BTW, just like running it open to the atmosphere), or to run the hose to a "breather box", which separates out the oil from the vapor. The oil then goes back into the case, and the vapor and air into the air cleaner of the carbs (if there is a fitting for it).

--DD

[halbl]

I agree with D Darling. VW makes a crank case vent system that consists of a small box mounted above the filler. Lines from each vent go into the box, which has a lid that overhangs to allow the case to breath, vent or whatever. A third line is a gravity return to the the opening on the rear of the filler. Makes a real mess at the track if one of the hose clamps comes off!!

[wjdunn3]

Thank You all for the quick response and good advice!