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Join Date: Nov 2000
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Breather hose setup for carbs?

On my '73 1.7L the PO installed a Webber single barrel progressive carb.

His breather hose setup was as follows. Take hoses from both heads, the breather box, and a plastic "container", and 'T' them all together with 1/4" copper water pipe. There are no filters or valves, such as a PCV valve I've seen on other, albeit F.I., engines. The hose on the air filter housing, and the intake (below the carb), are capped/plugged.

All my reference material only refers to F.I. setups. Surely everyone but me knows how this should be set up. Any help would be appreciated. Please be painfully specific (okay, maybe leave out clamp torque values ).

Thanks,
Tim
'73 914 1.7L Orange

Old 12-07-2000, 07:16 AM
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Your setup should work, but could be cleaned up possibly? I have seen catch cans duct taped to the top of the engine!!! My 2.8l four has both head breather hoses to a tee and then to a large catch tank mounted on the fire wall. This is not smog legal, but it is a 1973 and in CA it isn't checked anymore. The catch tank will work fine, but you will need to check and empty it periodically as it will cause oil spill and possible fire if the oil overflows onto the exhaust. This can easily happen if you have blow-by or accidentially overfill with oil. Good luck.
Old 12-07-2000, 09:17 AM
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What you described John is how mine is set up (only mine also T's into the breather box), so I guess it's okay. My catch tank did have some oil in it (1/4 cup - 1/10 of it's capacity), I'll have to keep an eye on that.

Two other questions:

1. Why can't the catch tank be mounted or routed in such a way that the oil would drain back into the engine, either into the heads or the breather box? I mean, all flatfour engines aren’t like this…are they?

2. What's the purpose of the capped air filter housing and the intake hoses? Surely they were put there for a reason.

Old 12-07-2000, 09:39 AM
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The whole engine is under pressure (at high RPMs, but a vac at low RPMs)so there would have to be some sort of check valve level detection system in the drain line to the block. But usually once oil leaves the engine such as to a breather catch tank it is considered dirty and should not be reused. The hoses going to the intake system on FI cars are to allow burning of the oil vapor before it collects. Good luck.
Old 12-07-2000, 10:29 AM
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I might be disagreeing with John here, but I'll note my observations, they're open to argument.
I run dual carbs, with a Bugpack breather box with three ports on it from the local V-dub shop. The box is mounted higher than the engine on the driver's side over the relay board and under the cover of the side ledge of the engine bay hatch, protected from the rain. Both heads are ported and run individually to two of the box ports, the third line is run direct from the stock oil filler box port. No oil ever collects in my breather box.
I did not run any hoses up to the carb air filters as I've read that oil added to the intake charge reduces the fuel octane level, to what quantitative degree, I don't know, but you're talking about increased potential for detonation. And there was another concern (and this is where I may be disagreeing with John's post).
I have noted the hose from the stock oil breather to be positive pressure at idle, and I think is was still so under revving conditions (I just don't remember for sure, and the car is in another state now, can't check). The head's hoses were positive pressure at idle, but negative under throttle revving conditions as the oil runs into the crankcase down the pushrod tubes, for sure. Which makes me wonder: what is happening inside the air filter boxes of people who vent their head's hoses there? as air is being sucked at cross purposes into both the venturies and into the port hoses? Possibly doesn't matter, but I still wonder.
Anyway, this is my setup, it's been maintenance free for years.

--John Lambert
Old 12-15-2000, 10:31 AM
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Sorry for the confusion, the vac in the engine is from the pcv valve connection from the intake plenum to the oil filler box. Most modified engines do away with this and vent to a breather can/box/catch tank. My race engine will leave a little oil (1/8 inch) in the bottom of the 1 qt catch tank after a two day race weekend and has gotten less since the rings have seated now. But I have a dry sump system which reduces oil blowing some due to less oil surface area exposed. I had a Bug Pak aluminum vent on an old VW bus and only cleaned it twice in 10 years but it was a little lower performance....

Old 12-15-2000, 04:14 PM
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