72' Type 4 Oil Bath Air Cleaner, Warm air Air Intake Hoses Options

[Ishley]

After 2 years of work....I've completed my '72 restoration...but one thing has me stymied.

I have an oil bath air filter... (pictured) and it has 2 air input points... one is a plastic goose neck and the other is a hose connection controlled by a vacuum system. The mysterious hose I think is supposed to run over to a connection point added to the engine tin...into a "hot air riser". I have no such connection point. I thought my motor was the original 1.7.... which I've now rebuilt into a 2056. I do not have a hot air riser tube.

The only place I've ever spotted a 72 with this type of a air cleaner is on a YouTube video of an original 72. https://youtu.be/w-c6Deg3fBU?si=FPjt3Fhg0lqMsaad Spotted at around 11:20 of this video. The video doesn't show where this hose terminates... but I assume into the mysterious "Hot Air Riser".

I also see in the PET diagrams they show this tube which would bolt to the engine tin behind the cylinder one location. I see a few ebay listings for this tube... but I've never seen it on any of the engines I've looked at.

Does anyone have insight into a hot air riser system.... that bolts to the engine tin behind cylinder one? I don't really think I need it... as this is really a summer only car... but I hate having this unknown empty input point on my air cleaner staring me in the face every time I pop the engine lid.

[wonkipop]

the stove pipe preheat for intake air is a funny one.

i know why the carb engined aircooled VWs had it.
carbies don't have a way to sense intake air temp.
so the old preheat tubes used to help with smooth idle. esp if ambient air temps were low. my old twin carb squareback had a version of the few different types they installed
if i remember right it was a flap that had a little counter weight.
at idle it would close cold air and open to warm air coming off the heat exchangers if i remember it right. there was a pipe ran down there. then when you opened the throttle the weight would be overcome and you only got ambient (cold air) intake.

but not really sure why they put them on EFI cars.
electronic fuel injection has intake air temp sensor that feeds into the ECU and control all that. At least L-Jet does.

Perhaps D-Jet never had temp sensor for intake air? dunno much about D-Jet in detail.