Baker, G. wrote:
(snip)
> I was putting SUs together yesterday and noticed that when I was putting
> the back stock air breather plate on my 56 MGA that both the carb flange
> and the back plate had two holes just above the holes used to hold the
> air breathers in place. Anyone have any idea what these are for?
> Thanks,
> Baker
Baker,
Those two holes provide a source for atmospheric pressure to the
underside of the SU piston. If you block those holes off (by using an
incorrect gasket, or putting one on upside down) the piston will have
much more difficulty rising in the damper in response to downstream
vacuum from the engine. This is much easier to explain with a diagram
of an SU, or you can trace the air passage when you have a carb taken
apart.
I have inadvertently covered up these holes when installing air filters
and had the devil of a time trying to figure out why the engine wasn't
running right.
Bill
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