Ryan,
Something doesn't add up. The vacuum advance tube (port) opening should
enter the carb throat slightly to the non engine side of the throttle
butterfly when the butterfly is closed or barely open. The tube should
NOT go down on the engine side of the butterfly.
This is called ported vacuum advance. There should be no vacuum on the
fitting at idle & the vacuum advance should be fully retarded. As the
butterfly opens, the port is progressively uncovered to permit vacuum to
be applied to the vacuum advance. Perhaps this is why "the vacuum which
comes from there is negligable". The vacuum advance should be shut off
at idle & progressively increase the advance as the the throttle is
opened.
A high idle setting (butterfly more than a little open) may cause some
vacuum advance which will screw up a timing light setting. That's why
disconnecting the vacuum advance is suggested when doing strobe timing.
At full throttle & higher engine loads the vacuum is low on the entire
engine & the vacuum advance is not advanced as much (more retarded) as
it should be. It will actually be zero vacuum advance at full throttle &
heavy load. The whole vacuum advance system is designed to give extra
advance under part throttle light load conditions to improve fuel
mileage, zero advance at idle, & zero advance at full load. Not all
engines are designed to work this way but the Healeys are.
If the port in question truly enters the carb on the manifold (engine)
side of the butterfly, you may somehow have the vacuum advance attached
to the wrong port. If so, you will have a hard time getting things to
work right, especially at idle where the timing due to the extra advance
will be much too far advanced. The typical vacuum advance range would
give something like 30-35 degrees too much advance at idle.
Dave Russell
Big Sixer wrote:
> On my HS6 carbs there is a small tube that sticks up where the vacuum advance
> line fits. I ran a wire down it to make sure it is open, however the vacuum
> which comes from there is neglibile. Any reason why? The tube goes down on the
> engine side of the butterfly valve, so there should be some vacuum force, but
> there isn't.
>
> Also, when is the vacuum advance most in use? When it is idling? When full
> throttle and the most air is going through?
>
> I don't get it: both why I don't have enough vacuum force and what it is meant
> to do?
>
> Help would be appreciated.
>
> Ryan
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