07-01-2018, 07:02 PM
(07-01-2018, 04:12 PM)Peter Naulls Wrote: The distributor is a DK4A so no issues with hidden resistors, but yes, I have replaced the rotor arm anyway.
I have now replaced the condenser with a new, tested one. No difference. Also replaced the distributor base plate with one that was in use a couple of months ago. No difference.
Andrew, I disconnected the coil and put a voltmeter (rather than a bulb) across the low tension wires. As I crank the engine it flicks between 12v and 6v - not what I expected. Does this suggest there is some leakage across the points? I'm beginning to think there is a short in the loom somewhere given that all the other components have been replaced.
Peter.
Hi Peter
The DC voltage between the points side of the coil and ground (i.e. across the points) when the engine is turned slowly should be be either nominally 12 volts with the points open or under about 0.2 volts with the points closed. The voltage from the switch side of the coil to ground will be 12 volts in either state, though it might be a fraction of a volt lower when the points are closed due to the current drain of a couple of amps causing some voltage drop in the ignition switch and wiring to the coil. I recommend using the starting handle so you can stop at exactly the right point.
Bear in mind that at the instant the points open there is a very short lived 400 volt spike across them, which hopefully your DC voltmeter will ignore.
If you are reading 6 volts across the points when they are closed it suggests to me that either your points have high resistance and their faces need cleaning, or there is a high resistance in the circuit from the earthy side of the points back to the engine block. In the latter case measuring the voltage from the earthy side of the points to the engine block can be instructive - I would expect less than 0.1 volts if all is well. I have found when cleaning points that a diamond spatula is good - if you use fine emery it's best to clean things up with switch cleaner (not WD40) afterwards. A strip of thin card soaked in switch cleaner and drawn between the points is useful.
Cheers, John.