> Reply-To: Robert J Donahue/DELCO <RJDONAHU@mail.delcoelect.com>
>
> I think the vacumn would stay constant because the piston is supposed
> to rise and fall to maintain a constant vacumn. So a blocked
> air filter would cause the piston to rise which also raises the
> needle which makes the mixture richer. Does anybody know in fact
> if the SU carburetor is senitive to the air flow resistance of the
> filter? If so it sounds like one should make sure the air filter is
> clean before adjusting the carb!
I understand that the vacuum which raises the pistons, in the SU carb, is
generated by the velocity of the airflow through the carb, not manifold
vacuum. Since a clogged air filter reduces the airflow the vacuum above
the piston is reduced, dropping the needle further down in the jet
maintaining the air/fuel mixture.
Of course extreme clogging will probably induce manifold vacuum through
the carb to the jet and cause flooding.
- -Mark "This post actually contains facts" Jurras
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