Thread: Question on coils and timing lights

Where are you picking up the positive and earth from or isn’t this timing light powered?

Sounds like the timing light is acting like a kill switch and shorting the circuit to earth. What kind of bike is it? And as Lappa said how are you powering the timing light - does it need a constant 12 volt supply to work (and does your bike have this?) Cheers

Light is connected to battery, as per instructions. Also tried a remote battery. Trigger connected to no 1, both at plug end and coil.

Try the light on another vehicle that has coil/distributor igniton.

Don't have another petrol vehicle, only diesel. The light is brand new anyway.

Maybe a leaky HT lead? Does it do the same on the other coil HT lead?

Assuming the coils are remote mounted and use HT cables to connect to plug, the primary thing that might stop the system working would be the pickup clamp exerting enough pressure on the HT cable to cause the connection between coil and cable or cable and plug cap to become intermittent. For this to happen, I would expect a relatively short HT cable with a curve in it, and the pickup being placed close to either end of the cable, straightening it at the entry point. The transition from cable to coil or cap is often just a small pin penetrating the end of the cable and a moderate amount of wear in the end of the cable and the pickup straightening the natural curve could cause the issue.

A more remote possibility is that the pickup 'loads' the coil somehow and damps the oscillation that the coil creates, or for an electronic ignition system, the firing pulse for timing light is feeding back to the control electronics in the bike and swamping it, preventing it from working properly.

The inductive timing light uses a small inverter to generate a high voltage stored in a capacitor connected to the terminals of the discharge tube. The signal from the inductive pickup is processed and a narrow very high voltage pulse is produced to trigger the the discharge tube. The discharge tube is gas filled and non conductive with just capacitor voltage present, but once the trigger pulse is present outside the discharge tube, it ionises the gas in the tube, making it conductive and the capacitor dumps it's stored energy into the tube, producing the flash of light. The whole process is very similar to professional level camera electronic flashes. Typical voltages that might be found are 1000V dc on the capacitor, and 4-8000V for the trigger pulse. If the ignition control electronics on the bike are close to the flywheel, or remote mounted but poorly shielded, then the 4-8000V trigger pulse could affect the control electronics.

A possible alternative might be to use an inline spark tester similar to the Briggs and Stratton style ones. These connect between the plug cap on the cable and the plug itself, and have a transparent chamber with a spark gap inside, allowing you to see the spark across the gap as the plug fires. They are a tester rather than a timing indicator, but will indicate the presence of a viable spark, where an automotive style inductive might interfere with the operation of the ignition system of the typical small engine.

A simple way to see if the HT leads & coils are leaking is to start the car/bike in a shed at night and turn all the lights off. You can actually see the spark the top of the plugs on good systems and what it realy does is show if there are any HT leaks in the system. Do that with the timing light connected and it may show some stupid behaviour in the leads, coils etc.

It's new, and you don't have any other vehicles to test it with...so you don't actually know that it is any good? I agree you should test also on #2 - you can't set your timing but you can see if it kills the engine.

Only thing I can suggest is to isolate the inductor part further using some silicon tubing or something like that. It's only trying to pick up a magnetic pulse after all. But try #2 first. If it kills the engine I'd be inclined to return the light.

Last resort test for the light is to connect to battery power and pickup to any other spark ign motor available, lawn mower, brushcutter, generator, outboard motor, chainsaw etc and see if that can fire the light.

Agree with Chris about firing up the bike in the dark and looking for arcing in the HT, provided that the motor is running, should also give an indication turning over with the starter, but you may not be able to position yourself to get a clear view.