Type4 - Crankcase breather

[Henrik_K]

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

[telford dorr]

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]

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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[Wildthings]

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.

[Henrik_K]

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

[XXX/Rx/RnR]

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]

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

The one in the middle with the filler cap would also do the same job.
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[Henrik_K]

Thanks for the advice.

Whats the difference between the different boxes?

Rgds, Henrik

[Wildthings]