I suspect the ignition timing will also depend on what cam type is fitted..? Seems like it is best to re balance the carbs to suit your own engine`s requirements. The vacuum pipe if fitted is usually a small diameter plastic pipe running from the inlet manifold to the distributor where it connects to a diaphragm and advances the ignition as determined by inlet manifold depression.. As best I can remember when unleaded appeared on the scene a few folk removed or blocked off the vacuum pipes..? If trying to use original settings on a modified engine would seem to risk less than ideal performance from it..?
Hope Arwyn jumps in soon... (-:
