Ignition components test, who is right?

[eavega]

Hello folks. I am trying to correctly diagnose a loss of spark on all three cylinders on my 1976 70 HP Johnson. I have three references for the various tests; OEM manual, CDI Troubleshooting guide, and Clymer manual. All three have similar but not equal thresholds for "Good" vs "Bad" with regards to resistance tests on the trigger and stator:

Clymer
Trigger "Pass" - 7.5 - 9.5 Ohms
Stator "Pass" - 555 - 705 Ohms

OEM
Trigger "Pass" - 7.5 - 9.5 Ohms +- 1
Stator "pass" - 625 Ohms +- 75.

CDI
Trigger "Pass" - 10-20 Ohms
Stator "Pass" 400-600 Ohms.

Who is right? I ask because the readings I got are spot on for what Clymer and the OEM Manual call for (I got 8.5 Ohms, 9.0 Ohms, 9.0 Ohms for the trigger circuits, 685 Ohms for the Stator), but are off on both counts for what CDI calls for. I was hoping to get some opinions as to whether the Stator and Trigger (Timer base) are still good on my motor and I should suspect the power pack.

I haven't done the DVA readings yet. I just got my DVA adapter in the mail yesterday. I'm hoping that the DVA readings will give me a definitive answer, but I was curious as to which guide I need to be paying attention to, since there is still a variation between the Clymer and CDI guides, and the OEM manual doesn't even contain the DVA tests, but rather use a "Neon Test Light".

Any advice would be greatly appreciated.

Rgds

 

[Haffiman]

Re: Ignition components test, who is right?

They are all correct!!
Clymer has just 'stolen' the values from the OEM manual.
When it comes to Ohm measurements is it a lot about temperature when measuring, and that is not stated anywhere??
The critical measurement is not the Ohm value, but the output peak Volt value.
The power pack triggers the firing signal at a certain pre-set voltage.
When that voltage is reached depends on a number of factors and one important one is completely missing in all manuals: Flywheel magnetism!!
(Usually measured by using a steel ball on a spring scale and see how much force needed to pull the ball off the magnet)
Take your Ohm readings for what they are, most important you get a reading and no short to ground.
The important ones are the Voltage readings.
Too low on stator, and the power pack will give a weak spark or even an intermittent spark.
Too low on the trigger, and it may not fire at all.

 

[eavega]

Re: Ignition components test, who is right?

Thanks for the reply!

The OEM manual did mention that the readings are at 70 degrees room temperature. Nobody else mentions temperature.

If I recall my physics correctly, temperature and resistance have an inverse relationship? Maybe CDI is taking that into account.

Onward to the peak voltage measurements.

Rgds