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YZ125 Dead Bike

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Ran into some problems today was wondering if I could get some help. So I just rebuilt the top end on my 2000 yz 125 all was fine broke the piston and rode around for about a hour or so. Yamaha oem kits are definitely the way to go, that's irrelevant. So I let the bike sit after riding and I came back to wipe it down with a little degreaser. I tried to crank it back up to run out the remaining gas and it wouldn't start :( . First thought was spark plug was fouled out so I took it out and put a new one. No difference still no spark when I kick over the motor. So I went to my local shop to get a new ignition cool and he said that isn't my problem it was my spark plug boot that's no good so I got a new one still nothing. So I checked my kill switch next. Unplugged it and kicked it over still no spark coming from my plug. What can cause this I checked my stator but I can't see it behind my flywheel. My wire harness seems to be good no wires are broken or anything. I'm about to throw in the towel with this one I have no clue what to do next. I also noticed my last plug was the electrode melted off. My top end has a lot of compression still and my piston doesn't seem to look damaged so my guess it ran hot and melted or maybe the jetting is off. I recently rebuilt the card and replaced everything inside with the parts from the carb kit. Can this have something to do with the sparkp plug melting?

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If you have zero spark even hand cranking the motor with the spark plug out but attached to the boot then you definitely have a electrical problem. Open up the stator side and ensure that the flywheel isn't loose at all and that it turns correctly when you cycle the motor with the kicker. Still no spark then you're gonna have to start troubleshooting. Check all the leads and make sure nothing is grounding out, buy a flywheel puller and  take off the flywheel so you can inspect the inside of it and the stator. If it all checks out to spec and still no spark then your coil/CDI is next since you replaced the spark plug boot/lead already.Hopefully the guy at the shop will let you return anything that doesn't turn out to be the problem once you replaced it with a new part.

 

I had a 2t that wouldnt kick over because the flywheel came loose and sheared the woodruff key off the stator side and came out of time, but i could still see spark with the plug out of the head and connected to the lead.

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I checked the fly wheel isn't loose and it looks clean inside there. I couldn't take off the fly wheel I don't have the tool yet, I'm about to get one on eBay. My wire harness does have a bunch of black wires connected to each other with a crimp. I saw that when I first got the bike but I just covered it with black tape and the bike was running fine. The mechanic at the shop said my timing could probably be to advanced how can I check that?

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Local shop should have a fly wheel puller, otherwise motosport.com or rockymountain has them for about 10-15 bucks. Even if the timing is advanced you should still see spark. Did you take the plug out of the head, connect it to the spark plug boot/lead and crank the motor while looking at the plug? You should see spark regardless of what time is set. If you see no spark, no amount of timing is going to fix that. If you see no spark you have a problem somewhere in the electrical. Whether that is with the flywheel/stator or with the coil/CDI is what you have to figure out. 

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 My wire harness does have a bunch of black wires connected to each other with a crimp. I saw that when I first got the bike but I just covered it with black tape and the bike was running fine.

This is probably where I would start looking. This is never a good sign.

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My guess is the coil cause the ends that serve as the ground are rusted out. So I'm guessing it's not gettin a good ground or just not good at all. I'm just gonna have to start replacing parts, starting off with the coil. I can't find any new stators on eBay I'm just gonna have to wait it out. I don't want any aftermarket parts rather get oem parts.

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I'm gonna try to check my connection I noticed a lot of them are real dirt and rusted so I'm gonna clean them and see if I get lucky. I hope it's just my ignition coil they have one for $70 new on partszilla. Thanks for the sites I always went to Motorsport but I don't like ordering from them.

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I'm on my phone I don't know how to tag you guys. @maniac998 I took the three wires apart and reconnected them with a good audio connecter. It didn't make a difference I'm just gonna buy a new stator and see if that's my problem. I'm also considering getting a new wire harness and ignition coil.

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Sparkplug melting is from the combustion chamber being super-heated, probably from a lean condition causing detonation too. Is your timing stock? Or did you move it when you rebuilt the engine last?

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I didn't do the last rebuild but I noticed they had some marks on the stator that weren't lined up with the mounting screws. So I loosened it and lines them all up no difference. I think my jetting is off because when I get wide open on the gas and let it go I hear a lot of popping as if it were backfiring. This bike is killing me though. I've been dying to take it out, but she's been in pieces waiting to get fixed.

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