Triumph Repair: lost spark when engine cranks, ballast resistor, triumph spitfire 1500

Question
Jim ,it appears to be a stock lucas eid distributor the coil looks newer and has no external resistor, not sure of it's history or voltage.thanks again for your help.Dave
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Followup To

Question -
Dear Jim, My son and I are restoring a 1978 Triumph Spitfire 1500. We got the car running but now lost spark when engine cranks,there is a strong spark out of the coil when the key is turned off this spark travels through to the plug it happened to stop by.The rotor does turn, and the coil seems to test out.The engine did back fire when it quit.Any direction would be greatly appreciated.Dave

Answer -
Dave,

In the stock setup you have a 6 volt coil and a ballast resistor in series with the coil on the main ignition circuit.  

When the starter solenoid is engaged the ballast resistor should be bypassed so the coil sees the full battery voltage.  What is sounds like is that somehow the coil isn't seeing the full voltage while the engine is being cranked.

Which ignition system are you running?  The stock Lucas "Opus" system, or another?

Cheers,

Jim  

Answer
Dave,

A couple of thoughts for trying to pinpoint the problem.

First off, get a decent multimeter and keep an eye on battery voltage as you crank the engine.  

The Lucas electronic ignition replaced the function of the points with a magnetically triggered transistor pack.  The problem is that unlike a points setup, once the voltage drops too low the Lucas unit will stop sparking.

At the same time you're checking the battery voltage disconnect the coil lead from the distributor cap and wedge a spare sparkplug into the end, grounded on the car body... the brackets supporting the clutch and brake master cylinders is a good area to look for a prop point.  As you have your assistant crank the engine verify whether or not you're getting any spark from the coil.

If the voltage is reasonable and you're not getting any spark then it's possible that the Lucas unit has failed.  

If that's the case there are several alternatives.  One is to return the car to a points type distributor.  Another is to fit one of the aftermarket units such as a Pertronix ignition system.


Cheers,

Jim