Coil Test - Need Some Input

ilbikes · Post by **ilbikes** » Sun Sep 13, 2009 8:56 pm

Hi fellas, I'm tracing down a "dead" ignition system on my "new" 1974 GT750. I have the newest NewTronics optical box, but no spark.

The 3 Orange wires are the switched 12 Volts - they are hot whenever the key is on and the handlebar switch is at the RUN position - check. I've go 12.28 volts there, so far, so good.

When checking the White, Yellow, and Black wires on the coils, I'm getting continuity between the Black/Orange, White/Orange, and Yellow/Orange wires in the connector at each coil. I checked 3 different sets of coils and all are the same. Should there be continuity between each coil's feed and igniter circuits? I'm getting 12.28 volts on the White, Yellow, and Black wires on the coils when the Orange feeds are connected. I thought the Orange stayed "hot" and the Black, White, Yellow timed the sparks.

What am I missing?

Thanks for the inputs.

Gordon

Suzukidave · Post by **Suzukidave** » Sun Sep 13, 2009 9:59 pm

Gordon , you might recheck the wires going into the control box .

tz375 · Post by **tz375** » Mon Sep 14, 2009 12:39 am

Gordon, so far you are right. Power goes from red into switch to Orange out to the coils. the white etc coil leads go to the points normally, and should connect to your "black box" on the Newtronics.

The old version of the instructions told you to unplug the coils and they failed to mention how the coils connect to the switching unit. I hope the new improved instructions cover that better.

Suzukidave · Post by **Suzukidave** » Mon Sep 14, 2009 7:16 am

I havent seen one of the new units but for the old ones all you had to do was attach the supplied patch cord to the coil plug so you couldnt have a problem there , but the group of wires from the points plate had to be attached to the box in the correct order by color or the unit wouldnt work so thats my reason for my suggestion .

tz375 · Post by **tz375** » Mon Sep 14, 2009 9:39 am

Gordon,

Coil resistance is about 5 ohms, so you would expect to see almost full voltage after the coils.

In a points system the power flows from battery -> switch->kill switch->coils->points->ground

With Electronic ignition the coils connect to the Switch unit (black box) which is connected to the LED's which trigger the switches and allow the coils to connect to ground to charge the coils or to break that connection and fire the plugs.

With Newtronics, there are some questions about timing them. I know one GT750 rider who believes his unit retards at high revs. I know another who tells me that his has a shift in timing at around 1500-2000 rpms so that if he sets timing statically, it runs way too advanced. So I'd check the timing with a light just to be sure.