Pelican Parts Forums - Setting ignition timing and dwell in 1976 911s 2.7

Quote:

Originally Posted by NeedSpace (Post 7535144)

I may do the conversion at some point. I did convert my old mercedes to electronic ignition with great results. I previously had problems with my car in wet weather and not starting. The car has never run so well.

I am going to stick to points for now for the education of it. I want to learn more about how they work and how to tweak them. Also, to be honest, they haven't been much of a bother. That said, if they start becoming an issue, I'll yank em.

The breaker points operation is quite simple. Battery voltage is applied to the coil's positive end of its primary circuit winding. The opposite end is connected to the breaker points which ground the circuit. Dwell is read as the amount of time (in degrees) the breaker points are closed (charging the coil's primary winding). Since the coil's primary winding (wound around a laminated metal core) is creating a magnetic field around the secondary winding (many more windings wound around the outside of the primary winding), the instant the breaker cam in the distributor opens the points (at this point the condenser which is wired parallel to the breaker points absorbs some of the voltage spike hence protecting the points from arcing), the coil's magnetic field collapses inducing high voltage in the secondary winding. One end of the secondary winding is grounded and the other end is connected to the spark plug by virtue of where the secondary rotor is pointing.
Problems with this system include:
1) Pitted breaker points
2) Condenser over saturation
3) Worn breaker cam
4) Worn Dizzy shaft bearing
5) Binding mechanical advance weights and springs
6) Degraded vacuum retard dashpot (vacuum hoses)
7) Internal voltage leak between the secondary and primary winding of the coil
8) Degraded(carbon tracked)coil, rotor, dist cap and secondary ignition wires
9) Poor primary voltage supply from ignition switch/fuse box
10) Poor distributor/breaker plate ground

There are many more examples of breaker system failure and some defy reason. Some of the popular diagnostic practices include:
1) Spraying water on high voltage (secondary ignition) components while engine is running.
2) Applying different 12 volt supply to coil's positive connection
3) Disconnecting CDI unit
4)Installing a redundant ground to distributor housing
5) Using a strong magnet to diagnose coil break down