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Type4 - Crankcase breather
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Henrik_K
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PostPosted: Wed Jun 03, 2020 12:22 pm    Post subject: Type4 - Crankcase breather Reply with quote

Due to oil fumes in engine room, I've decided to run a hose from the stock breather to my inlet manifold - below the carb.

The idea was that the vacuum would "suck" the fumes into the manifold - and as a side effect making a small vacuum in the engine, to keep oil leaks to a minimum.

Unfortunately, my engine backfires a lot with this solution.

What did I miss? will the oil fumes prevent a proper fuel/air mixture going through the manifold?

I previously tried to let the hose go to the airfilter - but theres not enough vacuum.


Any other solution?

Thanks
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telford dorr
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PostPosted: Wed Jun 03, 2020 12:34 pm    Post subject: Re: Type4 - Crankcase breather Reply with quote

What you missed is that you added a large vacuum leak, causing the engine to run lean - hence the backfiring. At a minimum, you need a metering valve or orifice to control the air flow, and you need to compensate the mixture so it isn't lean. This is not a trivial modification.

Might be better to fix the engine (pistons and cylinders) to stop the blow-by, eliminating the need for the extra venting...
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SGKent Premium Member
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PostPosted: Wed Jun 03, 2020 1:21 pm    Post subject: Re: Type4 - Crankcase breather Reply with quote

vent to the air cleaner and be sure to install a flame arrestor so you don't blow the engine up if you have a backfire with a flame front. You can add a catch can instead but you will need to drain it every so often of foam and oil or it will puke all over the engine bay. If you have a bus later than 1968 or 1969, you may run afoul of the law for venting crankcase gases to the atmosphere if you end up in any kind of vehicle inspection.
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I am not telling you what to, or what not to do. When a suggestion is offered, it is wishing you the best, & is based on my experiences as a mechanic, automotive machinist, & from racing in the era your bus came to life.
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Wildthings
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PostPosted: Thu Jun 04, 2020 2:28 pm    Post subject: Re: Type4 - Crankcase breather Reply with quote

What fuel system do you have?
What kind of breather do you have VW used multiple designs depending on the fuel system.
Pictures of your engine would be nice.
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Henrik_K
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PostPosted: Sat Jun 06, 2020 12:11 am    Post subject: Re: Type4 - Crankcase breather Reply with quote

My breather looks like this. I run carbs...

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XXX/Rx/RnR
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PostPosted: Sat Jun 06, 2020 5:41 am    Post subject: Re: Type4 - Crankcase breather Reply with quote

Swap to a breather from a 72-74 stock carb t-4. Breather hose is "T" into fuel vapor return to air filter. That way fuel vapor and oil gases are sucked into engine.
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busdaddy
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PostPosted: Sat Jun 06, 2020 8:24 am    Post subject: Re: Type4 - Crankcase breather Reply with quote

You need a breather box that looks like the one on the far left here:

https://www.thesamba.com/vw/classifieds/detail.php?id=2379121

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The one in the middle with the filler cap would also do the same job.
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Henrik_K
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PostPosted: Mon Jun 08, 2020 12:12 pm    Post subject: Re: Type4 - Crankcase breather Reply with quote

Thanks for the advice.

Whats the difference between the different boxes?

Rgds, Henrik
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Wildthings
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PostPosted: Mon Jun 08, 2020 1:11 pm    Post subject: Re: Type4 - Crankcase breather Reply with quote

Henrik_K wrote:
Thanks for the advice.

Whats the difference between the different boxes?

Rgds, Henrik


The two boxes on the right have PCV valves that are designed to be plumbed into the intake manifold.

The second box from the left is for FI and has a valve to control crankcase pressure. I lot of people who swap from FI to carbs do run this box.

The other two valves were for use with carbs, they have a baffle in them but no other restriction.

The cap that is on two of the valves is the oil filler used in some application.
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