No spark? Can I test the CDI?
 

My bike died the other day, it had no spark. I've replaced the plug and the coil, which means the next thing up the line is the CDI unit. But that's just a black box, is there any way to test if current is going to the coil or is it one of those times where all you can do is replace and hope that works?

A multimeter is essential
 

There is a useful fault finding resource within the electrosport website:-
Diagnosis Center - Helping you Find the Problem - ElectroSport

Most discussion about electrical faults occur within the HUBB in the Yamaha Tech forum which has some good threads about many aspects.

Good luck!

Thank you Dave, the implication there is that Yamahas have frequent electrical problems, but I'm sure you're not saying that.

It always seems to happen to XT600s.
My XT225 is doing just fine, all fingers crossed.

Check the sensors - that is the input to the CDI.

There should be one that provides the timing signal - probably a coil that can be checked for continuity and insulation. Be aware that coils can get internal shorts that reduce their resistance.

------------------ After that I'd check the voltages on the CDI connector.

6 hours ago I omitted to mention a main resource in that earlier link - the fault finding flow chart, that is an excellent way of maintaining a logical thought process when looking at bike electrics (I like it anyway!).
http://www.electrosport.com/media/pd...ng-diagram.pdf

Check the HT lead between the coil and plug unless the new coil came with a new lead.....

Sensors next - CDIs going wrong is unusual and there are periperheral things like earth connections and the above that I would think are more likely culprits.....

First check continuity from the CDI to the coil...

You can also check that when you turn the engine over, the wire from the CDI is giving voltage to the coil...

What bike is it ?