Distributor problem

[Tony Griffiths]

The other day the Chummy just cut out and stopped. Juice is reaching the + contact on the coil but the ammeter only shows a discharge when the points are closed - and the car won't start. Any ideas before changing everything?

[Chris KC]

Electrics are hardly my strong point Tony. But the first thing I'd do is whip out a plug, reconnect the HT lead and ground it, so you can visually check whether the plug is sparking or not when the engine is turned over (I've spent many an hour trying to diagnose an "ignition problem" which turned out to be something else entirely).

[Tiger]

Tony
Ammeter showing discharge only when points closed in normal.
Advice from Chris is spot on.
But instant failure is often electrics

[PaulS]

You can also get Sparkrite ingnition testers which go in line with the plug lead and flash each time the spark occurs, handy to carry one or more with you.
Check all connections to your coil especially that it is earthed properly. Also try replacing the condenser which often go.
Another issue I have had is the conductor in the top of the distributor cap(on the end of a spring), this is quite easily knocked out of position or falls out completely.

[Howard Wright]

Hi Tony

A common issue is with the internal earth connection in the bakerlite base plate failing. Run a separate earth to the points post.

Cheers

Howard

[John Mason]

Hi Tony, I believe you have more than one seven in your family. Temporarily borrow parts and exchange them for yours one at a time such as coil, condenser, distributor cap. That way you can check your own parts with known good ones. That way if successful you will only have to replace one part. Remember to replace all borrowed parts and check that the car starts ok especially if it’s your wife’s car.
Also check for tightness the two screws that hold the baseplate. They earth the points.

John Mason.

[Charles P]

I had a recent electrical problem, as shown in the picture below (yes, my A7 runs a dizzy from a MM Series Minor)
The points that failed were bought last year from an online classic car electrical parts outfit, brand new and in a newly made box marked “Remax”. Not the Remax of old. 
Lesson learnt and I bought replacement parts from the Distributor Doctor which look much better quality. 

   

Charles

[john williams]

The Quickest way to check ignition out put. Remove HT lead from centre of distributor. With ignition switched on, hold the end of the HT lead close to cylinder block, motor the engine on the starter, you should get a spark jumping from the coil lead to cylinder block. 
If not, disconnect the LT lead from the distributor, switch on ignition, repeat HT lead spark test by flashing LT lead to earth. If you get a spark, point condenser or distributor earthing if suspect. If no spark, check coil SW feed with ignition on, and CB coil connection, then CB lead continuity to distributor.  If all the coil connections and leads are correct, the coil is suspect.

[Tony Griffiths]

Thank you all for the help and advice - greatly appreciated. I'm going to start swapping parts from the other cars this weekend and will see what happens.