> A fellow MVT club member has a "new" TR4A that seems to run
> well, but is down on power. We've determined that the vacuum
> advance on the dizzy is not receiving any vacuum, but can't
> figure out why. Using a vacuum gauge attached to the PCV outlet
> of the intake manifold, it pulls a steady 15" at idle. Moving
> the same gauge to the vacuum port on the HS6 SU reads ZERO at
> idle, and maybe 1" after reving the engine and letting it back
> down. We've sprayed starting fluid all around the manifold and
> carb gaskets with no obvious vacuum leaks, so where's it going,
> and why is there no vac at the vacuum advance port? Ideas anyone?
Well, there isn't supposed to be any vacuum at the port with the throttle
closed, and when you open the throttle far enough to uncover the port, the
manifold vacuum drops for the split second until you have to close the
throttle again to keep the engine from over-revving.
To do an accurate test, connect your vacuum gauge with a long length of
tubing, then lead it out from under the hood & prop it on a wiper or
something. Take the car for a test drive, where you can load the engine and
keep the throttle partially open long enough for the gauge to register.
But I think you're barking up the wrong tree, as the vacuum advance does
nothing at wide-open throttle (no manifold vacuum) and so has nothing to do
iwith maximum power output. Having a non-functional advance may make the
engine seem a bit sluggish at part throttle, but won't change full throttle.
Have you checked the valve and ignition timing ?
Randall
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