Ported Vacuum Advance

The correct vacuum advance source is important

An informative article expressing the importance of utilising the correct source of vacuum for the distributor advance. My understanding of the difference between manifold or carb ported is the effect on tickover. The manifold port provides a lot of advance on tickover which gives economy but a bit more lumpy tickover.

https://www.britishvacuumunit.com/ported-vacuum.html

Also the carb porting gives a quicker take up when accelerating from tickover.