The coils have 2 terminals on them -ign fed live and "switched" earth ,
The live feed (usually Orange
) is an ignition fed 12v positive live and is common to both coils
the switched earth will be something like Black
for the coil that fires 2&3 and white
for the coil that fires 1&4
with the wires all connected to the coils , it will appear like you have a 12v + both sides of the coil. As you turn the motor over with the starter , the CDI unit will momentarily ground the switch earth wires ( Black
) . This forces the charge built up in the primary windings to be dumped and create a spark at the plug.
This 'switching' is usually too fast for anything but a top of the range multimeter to detect - so you'll go round in circles trying to test a coil in this way.
To check the coils
- Do one at a time
- Leave the Orange & white wire connected to the coil.
- Disconnect one of the 'switched earth' wires from the loom , and instead use your own separate piece of wire .
- Connect one end of this wire directly to the switched earth terminal of the coil and clear the insulation from the other end to leave the wire bare
- Ensure that the 2x HT leads from the coil that you are testing are in good condition and firmly attached to the coil
- Put 2 x 'known good' spark plugs in the end of the HT leads.
- Rest the spark plugs against a good earth ( test with a volt meter )
Now the fun bit !
- switch your ignition on
- briefly flick the bare end of your new 'switched earth' wire across the negative terminal of the bikes battery - when this happens , both the spark plugs should give a healthy fat spark.
Go through the same procedure with the other coil.
What you are doing here is effectively bypassing the CDI as well as, the loom between the CDI and the coils. You are manually switching the -ve side of the coil in order to get a spark at the plugs
If you still get no spark ,and you've sure that all your connections are good - then you may have a dodgy +ve supply to the coils . You may well have 12v reading on your meter , but trust me - that means nothing if the current is too low , the resistance is too high or there is a break somewhere in the insulation .
Disconnect the Orange
wire from the coil , and instead run a wire directly from the positive terminal on the battery ( you've now bypassed the live feed all the way from the fuse box , through the ignition switch , and through the loom to the coils .
Again , flick your 'home made' switch earth across the -ve terminal off the battery -Again, you should get a fat spark at both
plugs ( at the same time)
If you still get no spark , then you have a problem with either the coil / HT lead / or spark plug that you are testing. You'll have to go right back to basics and start measuring the impedance and continuity of the coils - the specs will be in the manual. Failing that , it's a case of swapping items over ( coils / HT leads / Spark plugs ) with known good items.
Hope this helps