Manifold airflow question

[slow-lane-Matt]

I bought a solid new SP manifold on Ebay (£1 !) and though I'd de-coke it before fitting.

I poured petrol down one end expecting it to level out and flow to the other end...

...it didn't - so it got me thinking - either it's totally blocked, or maybe the two ends are not connected....

Knowing nothing about VW exhaust systems (but learning) I understand hot exhaust is ducted up via the two arms
to heat up the carburettor, but it looks symmetrical like hot air comes in from both ends/arms- in which case how is it meant to flow,
where does it come out...?

I guess I am missing something pretty basic, can anyone explain how it works.

Thanks

No a very good photo, the upper end/arm you can't see is dry

 

[subheatadey]

Sounds like the pre-heat tube all its just a tube to get warm to stop the carb icing up, mine was totally blocked so drilled a hole at the bend and used some thick wire or thin rod and filed a dlot stuck it on the end of a drill and bored my way through. They get coked up over years.

 

[kreemoweet]

The heat riser tube is supposed to be free-flowing, and the exhaust flows in one direction only, and that one-way flow depends on the use of a
properly constructed muffler (many aftermarket pieces are not) and correct installation of the tailpipe(s). The tubes tends to get blocked over time with carbon deposits and rust. Many older manifolds are a lost cause, and attempting to unplug them results in a holed tube and exhaust
leaking into the engine compartment. The tube is not round where it runs thru the aluminum cladding. A properly working heat riser is easily detected by the extreme temperature difference between the two ends.