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beetakingthe405

Help diagnosing no spark on 426

10 posts in this topic

Long time listener, first time caller...I've just recently started tackling this 426 I got last year and have run into a bit of a wall. I got it cheap so I knew there were going to be problems and I knew the PO was not a very smart person (welded a sportbike kickstand to the frame instead of buying a trail tech one...). So I cleaned the carbs, replaced the air filter, and replaced the spark plug which got it running. It didn't like to idle so I figured I'd start to tackle that issue.

 

I bought a thumb screw for the air/fuel mixture screw and also managed to find a full Pro Circuit exhaust for cheap. I took it out to the dirt, got it running but still couldn't keep an idle. i messed with the air/fuel as well as the idle speed and just couldn't find a happy spot. Then after only about 20 minutes of riding, I took the bike back to my truck to add some more gas to the tank, stopped the bike with the kill switch, and haven't been able to start it since.

 

I replaced the plug with an iridium one, still nothing. I also pulled the carb again and found out I had a 155 main (stock pilot, no bk mod). I replaced the main with a 168, going off what I saw on DynoJet's instructions for their kit and kind of what I saw on the jetting database. I also replaced my pilot just for good measure, staying with the stock 42. I checked the valves, which is something I've never done before, but I think I did alright. The exhaust cams were all tight by .1mm. Reshimmed, and made sure all the tick marks were lined up correctly and reset the cam chain tensioner correctly.

 

Since I took it to the dirt that one time and couldn't get it restarted, I haven't been able to get a glimpse of a spark. I tried to see if there was spark so I pulled the plug, grounded it and hand cranked the kick starter, but couldn't see anything. I may not have given it enough umph, idk. I couldn't discern whether there was spark or not. 

 

Today I went through the electrical check list and everything that should have continuity did, and when they shouldn't, they didn't. But for the resistances, I got some funky numbers. 

 

Primary coil resistance measured 0.5 to 0.7 and should be 0.2 to 0.3

Secondary coil measured 24-25kOhm and should be 9.5-14.3kOhm

CDI Magneto Pick-up Coil was fine at 296 (should be 248-372)

CDI Source coil 1 was 365 and should be 720-1080

CDI Source coil 2 was 0.2 and should be 44-66

 

I don't have info on the stator and can't get the flywheel off (I can if I have to, I just need to borrow tools), but I bought this bike as a "California street legal" bike, so the electricals are kind of a mystery. The PO said he was converting it back to dirt only and it was the owner before him that had it street legal. The flywheel is definitely stock but I can't see the stator so idk if it's aftermarket or not. The CDI plug and wire harness does have a yellow wire that is cut. Not sure what that's about, but I'm attaching a pic. 

 

I know it's a lot of info, but that's the full story. I've tried to read as many accounts of "426 no spark" or "426 not starting" as possible and I'm still stuck. Just wondering if there's anything glaring that I'm missing or if anyone can suggest some things I should test. I'll probably try to get to the stator this week and just see what it is. 

IMG_1544.JPG

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Just gonna talk to myself...I checked out a used coil on Craigslist. Took the calibrated multimeter from work with me and got the same numbers as my coil. Guy says the bike ran well before the engine seized, so I didn't buy the coil and will assume mine is fine. Next step: replacing the stator. 

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The stator is your prime suspect if the previous owner used an aftermarket rewound unit the adds a lighting coil to the original YZ stator.  Such setups are notoriously unreliable.  The stock stator has only four poles, and was intended to be enough to operate the ignition and nothing else. "Adding" lighting coils doesn't add anything, it just takes away two coils from the ignition and converts them for lights, leaving the two remaining coils to do the job of sparking up the engine.  The problem is that unless they are wound with lighter wire, they can't produce the energy required to do that job, and if they are, they break frequently.

 

The "right" way is to substitute the larger stator and flywheel from a WR model, but that can involve a modification to make the stator compatible with the YZ ignition.

 

http://www.thumpertalk.com/topic/900815-yz426-rebuild/page-3#entry9517821

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The stator is your prime suspect if the previous owner used an aftermarket rewound unit the adds a lighting coil to the original YZ stator.  Such setups are notoriously unreliable.  The stock stator has only four poles, and was intended to be enough to operate the ignition and nothing else. "Adding" lighting coils doesn't add anything, it just takes away two coils from the ignition and converts them for lights, leaving the two remaining coils to do the job of sparking up the engine.  The problem is that unless they are wound with lighter wire, they can't produce the energy required to do that job, and if they are, they break frequently.

 

The "right" way is to substitute the larger stator and flywheel from a WR model, but that can involve a modification to make the stator compatible with the YZ ignition.

 

http://www.thumpertalk.com/topic/900815-yz426-rebuild/page-3#entry9517821

 

This is exactly what I was looking for, and from exactly who I thought it'd come from. Ok, that's comforting to hear. I will probably try to replace it with an oem yz stator because I can't find a wr one on ebay or craigslist around me. I'm just trying to get the thing running reliably and can work on lighting later. Thanks Grayracer, you were my only hope. 

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Cdi sounds like it's fried. Pretty common and I've actually had that happen on my 426. Used ones are cheap, and worth getting to have a spare if it's not it

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So I bought a stator off ebay, resistances checked out according to the manual. Now with everything back together, and with the idle adjusted so a 3/32 drill can fit under the slide (something I read today), I can get it to snap crackle sometimes, but no pop pop pop. If I turn the air fuel mixture in, to about 3/4 turn out, it seems to react better, but still not starting. Besides trying to bump start it, I can't think of what else to try.

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Oh mother fuuuuuuuuuu....the manual has a typo and I followed the wrong distinction. I thought the intake was the exhaust and the exhaust the intake...You are correct, my exhausts are both at .15 and they should be .2. I'll put my intakes back to the .1 that they were before I reshimmed them to .2 and then report back. Hopefully that's the ticket. Thanks

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