Yamaha DT50 no spark and hot coil

[Guest]

Hi all,

I have a 1987 Yamaha DT50 MX here, CDI ignition, the wiring looks like it has been a bit 'home made' in places but it must have worked before as the previous owner was riding it until it was left in his shed for a couple years.

Anyway, the issue I have is that when I turn the ignition on, and kick over the engine, there is no spark visible. With the ignition on, the coil also begins to warm up. I have replaced the coil and it has a new 6V battery.

What could be causing this and are there any tests I could do to diagnose it, I have a multimeter.

Many Thanks,

Henry

[Joeman]

Think your year of bike still has points. If the coil is getting hot it would suggest the points are not separating and the coil is just staying energised.

The spark happens when you cut the power to the coil.

[Matt Strange]

Joe is right about the coil not being triggered, but you say it has CDI, so you will have a crankshaft pulse generator of some sort - probably a "hall effect" sensor. It produces a small current, usually around 1volt and this needs to get back to the bike's ECU to trigger the coil on/off. Maybe even just sent to the coil as some ignition systems are very basic.

You'd need to check to see if:

1. signal is there.

2. If not, is it a physical issue i.e. is the tip of the sensor broken, the mark or tab on the crank is o.k., the connector/wiring is o.k.

3. If you have a signal but no spark, you need to check the ecu. With the ignition on, you need a paper clip inserted into the multiplug on the ECU at the correct pin for the crank sensor input (Be very careful doing that, insert it with the ignition off). What you do is lick your fingertips, place one on the Battery+ on your bike and the other on the paper clip. Sounds silly but your body acts a resistor and will limit the voltage to about 1v, the same as a healthy pulse generator circuit.

This should produce a spark at the HT lead/spark pulg each time you touch the paperclip.

If the bike doesn't have a proper ECU, then you need to find the correct input on the coil.