[Rick Parker]

As Wayne described the light springs will often allow the weights to move at a relatively low RPM or because they allow static movement of the weights with the springs fully retracted. This will cause some of the available advance to be initiated before you get above the actual idle speed, thus limiting you to only have available 17 or 18 degrees of distributor advance. Sometimes because they have very little tension (light springs) the timing will fluctuate at low idle speed causing the idle to "Hunt" ie: raise up and down a little as the timing moves up and down a couple of degrees, this becomes worse and more exagerated with a long duration cam, open plenum manifolds and big carbs. The tangs on the base plate (attached to the shaft) can be moved a little to take up some of the free length of the spring and tweak the advance rate a little. If you are near a shop with a distributor machine (old school) it is much easier to create the curve you desire. Doing this is a dying art.