Timing light shows the same position for all the ignition lines.

[tavacska]

I am tuning with 1977 1150 inline 6 cylinders.

When I use timing light with the top cylinder.
It shows
1. 4 degree BTDC for primary pick up. ( manual suggests 4-6 BTDC).
2. 20 degree BTDC for max advance timing. ( Manual suggests 21 degree, but 20 degree maybe good too according to the gas difference with 30 years before).
3. I set up temporary idle position that the timing shows 1 deg BTDC.

Then I put the timing light to other ignition lines at the idle position. It shows 1 degree BTDC for all the cylinders.

How can that happen?
The trigger seems to be good, because it does send the signals. Each time the ignition happens, the coil send the arc to the distributor cap house, and then all the lines got ignition. It confuses me a lot.



But, when I do the manual cranking and pull out all the plugs and ground them, I can hear the ignition arc one by one, 1 -4 -5 - 2- 3 -6. I just don't know why the timing light can not show me the same results.

 

[Chris1956]

Not sure what to say. I have never checked the ign wires other than #1, however, I would expect them to be 60* apart in timing. You would need to follow the firing order to see the 60* intervals.

 

[tavacska]

It turns out to be the interference of other lines signal.
I tested it by pulling all the sparks out.
The timing light I am using, shoot beam 6 times every cycle, even no spark arcs at all. It is too sensitive. Even I put the tested line isolated, it still shoots out all the signals. I guess the signal is there since at the distributor.

 

[jimmbo]

Don't worry about the timing at idle. the retardation of the timing is what controls the idle speed, not the carbs which are to be full closed at idle

There may be carbon tracks inside the distributor cap. When you pulled all the wires off the plugs to check the timing, did you ground them, or just left them dangling? I have never heard of a "too sensitive" timing light

 

[gm280]

If your timing light is an inductive probe type, you could put some tin foil around the probe and ground it to help shield other interference from triggering the light. Just a thought.