For those of you who are interested in the topic of what needs to be done to
convert from your ZS carbs to HS6 ones, here's a web page by Paul Tegler on
the subject: http://www.teglerizer.com/mgstuff/a_stumble_at_cruise.htm .
Contributors to this web page claim that there is a difference between
connecting your distributor retard diaphram to the throat of your SU carb
and connecting it to the manifold. You probably need a vacuum guage or
manometer to measure the differences as a function of engine load and speed.
Here's one such contribution from Barney Gaylord, and may explain why just
connecting the retard distributor port to the manifold may work on '74 TR6s:
>At 10:46 AM 2/1/2001 -0600, Rick Lindsay wrote:
>> The original designs for vacuum advance used a port on the carburetor
that was connected to a small opening in the throat of the carburetor. ....
As the throttle is opened, the vacuum rises (depresses?) and the vacuum
advance module goes to work. ....
> > .... Newer designs have a vacuum port on the inlet manifold rather than
the carb. That port shows pretty strong vacuum even at idle. My car has
BOTH ports. Which method of applying advance is BETTER for my engine and my
application? ....
>The method ported from the manifold uses a different distributor, which can
be thought of as "vacuum retard" distributor. The vacuum from the manifold
is high at idle and holds the distributor in a retarded position. When you
open the throttle the manifold vacuum drops, allowing the timing to advance.
You need to use whichever port is appropriate for your distributor. Or
conversely, for those who do not have both ports, you need to use whichever
distrubutor is appropriate for your existing port.
>Barney Gaylord
>1958 MGA with an attitude (and no vac Mallory dizzy)
> http://www.ntsource.com/~barneymg
Jerry Shaw
'74 TR6 CF20490UO Saphire Blue
'66 Spitfire MKII FC70664L BRG
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