It slows down most likely because the engine manifold vacuum is diminishing
under load. That is, assuming that all the linkages were properly tightened.
Many cars with vacuum operated SC used a combination of manifold vacuum and
ported vacuum (from the venturi of the throttle body). The ported vacuum is
zero at idle but increases with engine load.

Not the same if an electric one is used.


"micven55" > wrote in message
lkaboutautos.com...
>I added the vacuum type to my car and it works ok. As soon as the road
> starts heading up the car slows and won't kick down unless I stomp on the
> gas myself. Once it has kicked down the car will climb back to the set
> speed without my foot on the gas and once the road flattens out it will
> shift back up again. I don't know if the electric ones have the same
> issue, but it's much better than nothing.
>