2015 yz 250 odd problem

yamirider287
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yamirider287
Edited Date/Time 8/12/2015 3:18pm
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2 hours sometimes sometimes 5 hours sometimes 1 hour and then all of a sudden it will run horrible. Poppin and back firing and just bad. Have changed stator coil pack an cdi and it still will do it. Carb is clean and reed cage is perfect. If ANYONE has had this please help me.
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The Narrator 8/10/2015 6:28am
8/10/2015 6:28am
yamirider287 wrote:
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2...
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2 hours sometimes sometimes 5 hours sometimes 1 hour and then all of a sudden it will run horrible. Poppin and back firing and just bad. Have changed stator coil pack an cdi and it still will do it. Carb is clean and reed cage is perfect. If ANYONE has had this please help me.
long shot here, but..

on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere in the cyl. i've seen an 02 CR250 do this.

but before i did that, i would change the wiring harness. also, check the ignition wire and spark plugboot. make sure they're secure and water tight.

Crush
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Crush 8/10/2015 6:30am
8/10/2015 6:30am
Fuel is good? Moisture in it?
yamirider287
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yamirider287 8/10/2015 6:34am
8/10/2015 6:34am
yes fuel is 110 octane with klotz r50 and we have checked through wiring harness tested wires to see if there was bad ground or connection and everything checked out. And its never consistent . It will run horrible and then the next day it will start right up and run perfect.

The Shop

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themrtoad
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themrtoad 8/10/2015 6:46am
8/10/2015 6:46am
Sounds like water in the fuel to me
gsxr6
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gsxr6 8/10/2015 6:46am
8/10/2015 6:46am
Sounds stupid, but unplug the kill switch and ride. Can't count how many times I have seen a bad kill switch have a guy pulling out hair. Your description is similar to the ones who had a wonky/ intermittent kill switch issue. Hopefully u haven't tried this already.
Muscle-Milk-KTM 8/10/2015 6:51am
8/10/2015 6:51am
gsxr6 wrote:
Sounds stupid, but unplug the kill switch and ride. Can't count how many times I have seen a bad kill switch have a guy pulling out...
Sounds stupid, but unplug the kill switch and ride. Can't count how many times I have seen a bad kill switch have a guy pulling out hair. Your description is similar to the ones who had a wonky/ intermittent kill switch issue. Hopefully u haven't tried this already.
That could well be it. I had that exact same problem, sometimes it was fine then the thing was cutting out & popping & farting. Took the kill switch off & hey presto, bare wire shorting out on the bars.
woodsracer667 8/10/2015 6:54am
8/10/2015 6:54am
possibly leaking left side crank seal
yamirider287
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yamirider287 8/10/2015 6:56am
8/10/2015 6:56am
Have tried plugs as well.
yamirider287
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yamirider287 8/10/2015 6:59am
8/10/2015 6:59am
gsxr6 wrote:
Sounds stupid, but unplug the kill switch and ride. Can't count how many times I have seen a bad kill switch have a guy pulling out...
Sounds stupid, but unplug the kill switch and ride. Can't count how many times I have seen a bad kill switch have a guy pulling out hair. Your description is similar to the ones who had a wonky/ intermittent kill switch issue. Hopefully u haven't tried this already.
Also have tried
yamirider287
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yamirider287 8/10/2015 7:00am
8/10/2015 7:00am
themrtoad wrote:
Sounds like water in the fuel to me
My sister has a 14 ktm 125 and we run the same gas can and everything an she has no problems.
yamirider287
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yamirider287 8/10/2015 7:00am
8/10/2015 7:00am
woodsracer667 wrote:
possibly leaking left side crank seal
That is the next attempt but wouldn't there be some noticeable oil inside the cover?
Muscle-Milk-KTM 8/10/2015 7:04am
8/10/2015 7:04am
woodsracer667 wrote:
possibly leaking left side crank seal
Possibly, depends if the stator cover is airtight. I have a 94 CR250 that stood for about 10 years in my garage. It has a Boyesen stator cover that we glue to get a more water seal. Anyway, I took the cover off one day & I noticed a small puddle of oil under the flywheel. I thought that's strange, pulled the flywheel off & I kid you not the crank seal was just sitting there. Never did it once run like it had an airleak.
Mx286
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Mx286 8/10/2015 7:07am
8/10/2015 7:07am Edited Date/Time 8/10/2015 7:07am
yamirider287 wrote:
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2...
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2 hours sometimes sometimes 5 hours sometimes 1 hour and then all of a sudden it will run horrible. Poppin and back firing and just bad. Have changed stator coil pack an cdi and it still will do it. Carb is clean and reed cage is perfect. If ANYONE has had this please help me.
The Narrator wrote:
long shot here, but.. on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere...
long shot here, but..

on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere in the cyl. i've seen an 02 CR250 do this.

but before i did that, i would change the wiring harness. also, check the ignition wire and spark plugboot. make sure they're secure and water tight.

Had someone tell me the 15 has a casting flaw in the cylinder. Supposedly your suppose to replate it when new. I found that kinda ridiculous but theirs did let go with about 3 hours. My buddy bought one recently and has around 10 hours as well with zero problems and no replate.
yamirider287
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yamirider287 8/10/2015 7:10am
8/10/2015 7:10am
yamirider287 wrote:
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2...
I recently bought a new two stroke 2015 250 and with maybe 10 hours on the bike its a nightmare. Bike will run perfect for 2 hours sometimes sometimes 5 hours sometimes 1 hour and then all of a sudden it will run horrible. Poppin and back firing and just bad. Have changed stator coil pack an cdi and it still will do it. Carb is clean and reed cage is perfect. If ANYONE has had this please help me.
The Narrator wrote:
long shot here, but.. on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere...
long shot here, but..

on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere in the cyl. i've seen an 02 CR250 do this.

but before i did that, i would change the wiring harness. also, check the ignition wire and spark plugboot. make sure they're secure and water tight.

Mx286 wrote:
Had someone tell me the 15 has a casting flaw in the cylinder. Supposedly your suppose to replate it when new. I found that kinda ridiculous...
Had someone tell me the 15 has a casting flaw in the cylinder. Supposedly your suppose to replate it when new. I found that kinda ridiculous but theirs did let go with about 3 hours. My buddy bought one recently and has around 10 hours as well with zero problems and no replate.
maybe ill check into that.
The Narrator 8/10/2015 7:15am
8/10/2015 7:15am
The Narrator wrote:
long shot here, but.. on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere...
long shot here, but..

on very rare occasions a cylinder will come off the production line with a casting flaw, which manifests itself a pinhole, somewhere in the cyl. i've seen an 02 CR250 do this.

but before i did that, i would change the wiring harness. also, check the ignition wire and spark plugboot. make sure they're secure and water tight.

Mx286 wrote:
Had someone tell me the 15 has a casting flaw in the cylinder. Supposedly your suppose to replate it when new. I found that kinda ridiculous...
Had someone tell me the 15 has a casting flaw in the cylinder. Supposedly your suppose to replate it when new. I found that kinda ridiculous but theirs did let go with about 3 hours. My buddy bought one recently and has around 10 hours as well with zero problems and no replate.
yamirider287 wrote:
maybe ill check into that.
yea, it's a bit of a Hail Mary, but watch that end up being it. hahaha
yamirider287
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yamirider287 8/10/2015 7:19am
8/10/2015 7:19am
Hahaha ya I am 19 and this is the first bike I have bought myself and its pretty frustrating looking at $7,000 boat anchor i will definitely try that tho.
yamirider287
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yamirider287 8/10/2015 7:20am
8/10/2015 7:20am
Wouldn't that be consistent failure tho?

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mx184
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mx184 8/10/2015 7:27am
8/10/2015 7:27am
Check all wiring connections, Pay close attention to the stator wires. Also the CDI should be located near the right radiator, make sure there is no antifreeze getting in any connection there. One more long shot, But I have seen it happen. Check the fly wheel we lost a magnet once on a polini man what a head scratcher. Carb vents clean? Last but not least check the stator mounting screws. Good luck and let us know what you find.
yamirider287
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yamirider287 8/10/2015 7:31am
8/10/2015 7:31am
Will do! Thanks for all the input. Wish someone would have this exact problem. Haha I can't be the only one in the united states with this problem.
mx184
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mx184 8/10/2015 7:35am
8/10/2015 7:35am
We ran 105 octane in his 2013 stock yz 250 and it did not like the fuel, jetting issue I suspect. try different fuel, Seems like the quickest fix but these intermediate issues are never fun. My first thought is Stator.
yamirider287
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yamirider287 8/10/2015 7:50am
8/10/2015 7:50am
Ya that was mine too. Thats why there is a brand new one in there. haha
cable
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cable 8/10/2015 7:54am
8/10/2015 7:54am
Does it do it when cold, or only after the engine gets hot?
yamirider287
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yamirider287 8/10/2015 7:58am
8/10/2015 7:58am
cable wrote:
Does it do it when cold, or only after the engine gets hot?
Never has done it cold. During a race everytime.
moore433
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moore433 8/10/2015 7:59am
8/10/2015 7:59am
My son's yz 85 was doing something similar and you'll never guess what it ended up being !!!

The main core wire that runs through the spark plug was broken. While running the core wire would separate a little from the bike bouncing around on the track and it would stutter and then run fine, then stutter again.
Pull your plug and pull up on the metal part that is coming out of the ceramic outside piece and make sure it isn't broken inside the plug.
yamirider287
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yamirider287 8/10/2015 8:01am
8/10/2015 8:01am
I have kinda checked that but i will take a closer look. But when it acts up sometimes it will for hours or minutes. Idk nothing is the same everytime it acts up.
WRH
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WRH 8/10/2015 8:10am
8/10/2015 8:10am
Generally back firing and popping are contributed to either stator/ignition or reeds going out. But since you have many good suggestions of what to check ...
In the most extreme case of "I can't figure it out" the answer I found was the fuel . Try draining all the fuel and of course the carb, then mix some fresh fuel, If your running a full race gas then try mixing a couple of gallons with 87 octane split 50-50 with the race gas and your normal premix oil. If your problem goes away then you have saved many many hours of troubleshooting. If it doesn't work then you know it's not fuel related.
oldmotoyamaha14 8/10/2015 8:14am
8/10/2015 8:14am
Make sure your gas cap is venting properly. A clogged vent can cause fuel starvation.
moore433
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moore433 8/10/2015 8:16am
8/10/2015 8:16am Edited Date/Time 8/10/2015 8:18am
My son came back twice saying it wasn't running right. Both times I blasted it out at the end of the pits and it was running fine.
He went back out and came back saying the same thing. I was getting a little pissed so I took it out on the track and low and behold he was right !!!
I went to put a new plug in it and that's when I discovered that the center main wire running down through the porcelain outside piece was broken. Put a new plug in and it ran great after that...
Good luck !!!

most of the time if a plug breaks, it's the ceramic part that breaks, but this time it was the actual metal part inside the plug.
yamirider287
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yamirider287 8/10/2015 8:19am
8/10/2015 8:19am
Ya i wondered about that too because sometimes after i ride it will sit there and whistle and make noise.

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