Message text written by Anthony Rhodes
>The vacuum tap in the carb is close to the edge of the throttle valve.
Pretty much under the edge when it is closed.
It LOOKS like it would have little vacuum when closed, and then the hole is
uncovered with cracking the
throttle open.
This would appear to be a vacuum advance, right?
<
Here's the tricky part. The SU and Stromberg throttles rotate in oppostie
directions! Therefore the vacuum advance port would be on the bottom on an
SU and on the top on a Stromberg.
>I also suppose that if the distributor is designed with vacuum retard,
then it essentially uses mechanical advance
only. And further, as you say, that you need less advance at
wide-open-throttle, then there is a little loss of
efficiency at part throttle with this design. Therefore I think I should
look for an advance-type distributor....
I don't think it is so much need advance at full throttle but you WANT less
advance. Otherwise you just set it at the advance you want and dispense
with the advance module all together. At wide open throttle there is no
vacuum and thus no vacuum advance. Your timing will be the same at wide
open throttle with or without the module. The only thing you miss is some
fuel economy.
Unless you can find a distributor with a vacuum advance you should just
leave it disconnected.
Dave
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