[Healeys] HD8 vacuum port

[Alan Seigrist]

Tom -

The vacuum port on all SU carbs is before the throttle butterfly valve.
That means when the engine is at idle, the throttle is closed, and
thus little or no air is going by the vacuum port.  That's why there is no
vacuum here.  You will only get vacuum at this vacuum port when there is
high speed air flow through the carb.

This is confusing even for me from time to time!

Alan

'52 A90
'53 BN1
'64 BJ8

On 7/28/07, T W <ah3000me at gmail.com> wrote:
>
> Hi,
>
> When my engine is idling, and I put my finger on the vacuum  port of
> the rear carb, the one that's connected to the distributor, I really
> don't feel any vacuum.   If I check the vacuum port on the manifold,
> the one that's connected to the brake booster, the vacuum is really
> strong.
>
> Is the carb's vacuum port so small that it's normal not to feel
> anything there?   Or could it my port be clogged or something?
>
> thanks,
>
> Tom