>Gidday,
>I have been following this thread for a while, because I started it. I am
>surprised there isn't anything definitive, but I appreciate there is a
>difference between ID and OD. I do however "not" have my head around why you
>would need a restrictor in any fuel return line, irrespective of engine type?
The 914 is different, it uses rotary fuel pumps which delivery far more
fuel than the engine requires. This is the reason the 914 needs a bigger
return pipe dia than the 912s. 912s have a mechanical pump,
displacement dependant on engine rpm so delivery is much more limited.
Excessive return flow would cause reduced fuel pressure, which might not be
enough to avoid fuel starvation. The Facet electric auxiliary pump also has
limited displacement and won't give enough pressure to compensate.
Incidentally, the limited displacement/flow rate also makes the engine more
susceptible to vapour locking because the pumps have no way of catching up
the deficit caused by the vapour. Hence the importance of the return pipe,
it bipasses the vapour quickly and gets cool fuel to the pump. The pump
absorbs heat from the gearbox, which is heated by engine oil.
BTW there is no such thing as a daft question. How else can one learn?
Graham
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