00 YZ426 - No Spark!!!

Hello everyone. I'm new to the forum and new to dirtbikes in general. I picked up a good shape YZ426. The owner said that the engine was just totally gone through with a new piston and valve job about 10 hours ago. He said that he went riding last weekend and it ran great as usual then when he went to start it up to load it back up, it wouldn't fire. Long story short, he got it home and it had no spark. He TOLD me that he tried his buddy's coil off his yz450f and it fired right up. SO, being the dummy that I am, I go out and order a new coil thinking I'd be riding soon. Well, the new coil didn't fix it!! So here's my dilema. I checked the stator pickup coil, and primary windings and got in-spec ohm readings per the manual. Then, I check the new coil, which obviously gave me in-spec readings for primary and secondary. I checked the kill switch and it appears to be working according to the manual. Now, I notice the Nuetral switch wires that come off the harness are cut? There's a white, red with stripe, and dark blue with stripe that are all just cut and hanging there. Then, a lone sky blue wire goes up to the CDI. I'm wondering why these are cut? Also, I'm running out of options to check. I'm not getting any juice to the orange coil lead at all when kicked over. Anything you guys/gals can share with me so I can get this thing running would be great!! By the way, the bike has great compression and is getting gas. Thanks!!!

The early YZF neutral switch had 4 wires on it, only one of which is used. The white, red/white, and blue/white do nothing in that system. The light blue tells the CDI when the bike is in neutral, and in response to seeing a ground at that wire, the CDI retards the spark slightly, modifies the advance map, and lowers the rev limit. In the original harness the above listed wires ran from the switch to a connector, and that was it, so in effect, they were always "cut off".

What you need to do is to download a manual, if you haven't got one:


Then, go through the entire test procedure shown, first verifying the presence of power into the CDI, and through it.

OK, the on cdi test that is for the TPS voltage. It says that you are supposed to get 5-6 volts DC when testing the blue and black wires. My question is how is it supposed to read this high when there is no input power? I'm getting a reading of like .007 volts. I have a feeling my CDI is bad.

OK, nevermind on the above. I think the TPS output from the CDI is working as I can get about 4 volts if I kick it over fast enough so I imagine running it will be within spec. OK. Now, what else could be cutting off the ignition? I am hesitant to buy a new CDI if I don't need one but I've triple checked everything. Thanks Sorry if I'm rambling on.

The TPS voltage is supposed to be checked with the engine running. You need to test the stator coils and the trigger coil. Then start by testing for voltage to the CDI, and then to the coil.

OK, I've tested the stator coils and trigger leads. All ohm readings are perfectly in spec with the manual. I know I don't have voltage going to the coil, but how do I check for voltage going to the CDI??

Check for stator output using an AC voltmeter at the Pink and Black wires, and at the Brown and Green wires coming from the stator.

Thanks for the help Grayracer. I tested AC voltage on both the green/brown and Pink and black. I'm getting voltage as I kick on both sets of wire. It goes higher depending on how hard I can kick it over. Do you know about how many ac volts I should be getting when kicked? Seems that I'm getting more volts one set of wires vs the other. Thanks!

No, I don't have any specs available for that. The two coils are different, so it doesn't seem odd they would produce to different voltages.

It's apparent that my CDI is ouputting good voltage to the TPS wires, but NOTHING to the orange and black coil wires. I'm guessing that I will try a new CDI. If that don't work, I'm stuck in the mud.

The trigger coil has to be functional, or you may see nothing at the coil.

When I test the trigger coil I get Ohm readings right in the middle of the spec range. Does this guarantee that it is working??

Leave the ohm meter plugged into it and crank it. You should see a fluctuation in the resistance once per rev. Some digital VOM's may not react quickly enough to pick this up. If yours won't, use any cheap analog meter for this test on the lowest scale you can use (i.e. 1 ohm rather than 10)

Thanks for the help. I found the problem!! I'm glad I didn't buy a CDI. Using your advise grayracer, I tested the pickup voltage and got VERY low readings every 5th kick or so. So, I pulled the stator cover off. The flywheel bolt came loose it ended up breaking the woodruff key in half!! So, I'm very luck that it didn't do any damage in there. I cleaned the flywheel up, put a new woodruff key in and torqued it back down. FIRED RIGHT UP!! Man this thing is faster than I thought it would be!! I came from a 450R ATV so riding a bike this fast if new to me. I love it so far though. Thanks for the help.

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