2015 Yz250f

bgpn35
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bgpn35 11/20/2015 6:55pm
11/20/2015 6:55pm
My father n law yz450 would run but would shut off after idling for a few seconds. It ended up being the kill switch. Maybe you could take it off and stall the bike out if it does fire up. Idk, just trying to help!
tyler.hettick 11/20/2015 6:58pm
11/20/2015 6:58pm
I tried unplugging the kill switch and starting it. Didn't make a difference. Every 20 kicks or so the bike does make a pop, sounds like it's back firing. Makes me think its getting an irregular spark? Unfortunately i do not think it is the kill switch. Thank You though
KNIGHT104
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KNIGHT104 11/20/2015 7:20pm
11/20/2015 7:20pm Edited Date/Time 11/20/2015 7:21pm
do you use cold start to start the bike maybe you forgot to push back in have you tried adjusting the idle? is your air filter oiled? does it have to much oil? just some ideas i have had to adjust idle on a few of these. may also need to check your valves
tyler.hettick 11/20/2015 7:25pm
11/20/2015 7:25pm
i have adjusted the idle many times. No different. It has a fresh air filter, well from two weeks ago. Ill go out and take the air filter off and try to start it without the filter. The bike has 18 hours, with desert riding hours and track time. I'm trying to eliminate everything else before pointing at the motor itself.

The Shop

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KNIGHT104
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KNIGHT104 11/20/2015 7:33pm
11/20/2015 7:33pm
also check your gas tank vent line make sure its not plugged up
tyler.hettick 11/20/2015 7:42pm
11/20/2015 7:42pm
I have taken the vent line off during this time of diagnosing to eliminate that as a problem. I'm about to just take it to the dealer and eat Ramen for the next month
KNIGHT104
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KNIGHT104 11/20/2015 7:46pm
11/20/2015 7:46pm
its possible its a weak fuel pump then
tyler.hettick 11/20/2015 7:51pm
11/20/2015 7:51pm
I was thinking possibly a bad injector or fuel pump. I dont know how to check either of those items. I know its getting gas, thats about it
kmk371
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kmk371 11/21/2015 3:31pm
11/21/2015 3:31pm
I just had this same problem with my 2014 250sx and couldn't find any information on it. Was getting spark, fuel, air, compression, good connections, etc. All the things you should look for. The stator was putting out all the correct numbers when I tested it but I finally replaced it just to see if that would fix it. Bikes been running fine ever since. I suppose once the bike gets hot somehow the stator gets fried. One of those weird voodoo bike problems. Hope this maybe helps and you can get your bike fixed
slackinoff
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slackinoff 11/21/2015 5:54pm
11/21/2015 5:54pm
I had a similar issue with my 14. Take the plug out, clean it, kick the bike over while plug is out to clear cylinder, put the plug back in and give it a hell of a kick. I mean really kick it hard to turn it over quick. Don't touch the throttle while kicking....but be ready to catch it when it fires. Don't let it die. Adjust idle when warm.
Factor E
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Factor E 11/21/2015 10:26pm
11/21/2015 10:26pm
From you saying that you get a pop after a lot of kicks makes it sound like its a timing issue. Check your timing marks on the cams and at the fly wheel. Could be cam chain jump or if the marks don't line up at the flat wheel the woodruff key might have sheered and the flywheel moved on the crank.
lumpy790
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lumpy790 11/23/2015 6:20pm
11/23/2015 6:20pm
what is the compression? Not it feels like ... but an actual reading off a gage?

FYI 5 PSI will blow your finger off the hole.
tyler.hettick 11/23/2015 7:43pm
11/23/2015 7:43pm
Thank you for all of the posts. I recently went out and tried what slackinoff suggested, with pulling the plug again and clearing the cylinder. That didn't get it started. I plan to pull the throttle body off on Wednesday and clean it. I haven't actually done a pressure test for compression. Ill get the compression reading before i tear it apart to clean the throttle body.

Honestly if i can pinpoint that it is a motor issue i am more than fine with that since the dealer extended warranty will cover that. I already spoke with the dealer about the issue, and they have no problem diagnosing it. The only area for concern with that is if they find an issue that turns out to be a "non wear part" then it is on me. But if they diagnose that it is the stator, or it is some other electrical issue, then that is covered. I am worried about them spending 4 hours diagnosing it and then pin it on me. I wouldnt be able to cover the repairs at that point, hence why i am trying my best to diagnose it from home.

Once again, thank you for all of the replies. Once I try these ideas ill update everyone.
xnationalwrench 11/23/2015 9:32pm
11/23/2015 9:32pm Edited Date/Time 11/25/2015 7:52am
1st Suggestion:: Buy beg or steal the official shop manual. Check the output of the fuel pump, throttle body, and injector.
lumpy790
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lumpy790 11/23/2015 9:46pm
11/23/2015 9:46pm Edited Date/Time 11/23/2015 9:48pm
tyler.hettick wrote:
Thank you for all of the posts. I recently went out and tried what slackinoff suggested, with pulling the plug again and clearing the cylinder. That...
Thank you for all of the posts. I recently went out and tried what slackinoff suggested, with pulling the plug again and clearing the cylinder. That didn't get it started. I plan to pull the throttle body off on Wednesday and clean it. I haven't actually done a pressure test for compression. Ill get the compression reading before i tear it apart to clean the throttle body.

Honestly if i can pinpoint that it is a motor issue i am more than fine with that since the dealer extended warranty will cover that. I already spoke with the dealer about the issue, and they have no problem diagnosing it. The only area for concern with that is if they find an issue that turns out to be a "non wear part" then it is on me. But if they diagnose that it is the stator, or it is some other electrical issue, then that is covered. I am worried about them spending 4 hours diagnosing it and then pin it on me. I wouldnt be able to cover the repairs at that point, hence why i am trying my best to diagnose it from home.

Once again, thank you for all of the replies. Once I try these ideas ill update everyone.
a motor needs 3 things to start. Spark, fuel and compression. Which is missing?

Take the air filter out and squirt some starting fluid down the intake and kick. If it starts and then dies its fuel.

tell me about this warranty. Dirt bikes come with no warranty and if it did .... your tinkering around would void a warranty.
tyler.hettick 11/24/2015 9:05am
11/24/2015 9:05am
When I bought the bike from the dealer, they offered a 3 year warranty/insurance coverage on the bike. Up to $7000 if it's stolen, and free labor and replacement of non-wear parts. If the swing arm cracks, I get a new one. If the frame cracks, I get a new one. If the motor fails, I get a new one. But if the fork seals go bad, that's a wear part. Tires are wear parts, etc.

I asked a lot of questions about it, and have called and talked with the service department about this issue. If they diagnose it and it is a TPS or a timing issue, then it's covered. If I had money, then I'd have no problem having them diagnose it.

I just don't want them to spend 5 hours diagnosing it and it was something like the throttle body is gummed up, or something of that nature. Then I would have to pay back the labor and stuff.

I was just trying to do everything I could to make sure it isn't something that can be my fault, so that I'm not out the service money and parts.

Tonight I will try the staring fluid before I check the compression. Thank you for all of your help
tyler.hettick 11/27/2015 4:05pm
11/27/2015 4:05pm
Tried using starting fluid.. no difference. Ran a compression test with the throttle fully open, and was about 66psi. I left my manual at school, so i dont have it here to reference. I feel like that compression is low. Does anyone know about where the compression should be?
CarlinoJoeVideo
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CarlinoJoeVideo 11/27/2015 5:17pm
11/27/2015 5:17pm Edited Date/Time 11/27/2015 5:23pm
tyler.hettick wrote:
Tried using starting fluid.. no difference. Ran a compression test with the throttle fully open, and was about 66psi. I left my manual at school, so...
Tried using starting fluid.. no difference. Ran a compression test with the throttle fully open, and was about 66psi. I left my manual at school, so i dont have it here to reference. I feel like that compression is low. Does anyone know about where the compression should be?
So a little edit here: After looking online for more info, seems like it's the percent lost from what you pump in. So depends on your input pressure.

Pit Row

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tyler.hettick 11/27/2015 5:36pm
11/27/2015 5:36pm
It has 13 hours on the motor, with trail riding hours on it. Stock motor, exhaust, etc.
mb
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mb 11/27/2015 9:22pm
11/27/2015 9:22pm
If you're only getting 66psi I would bet that you slipped time, doubt you have any piston/cyl issues.
tyler.hettick 11/28/2015 4:11pm
11/28/2015 4:11pm
If it was running and then died do you think it could be valves? Would that account for such low compression?
slackinoff
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slackinoff 11/28/2015 8:22pm
11/28/2015 8:22pm
tyler.hettick wrote:
If it was running and then died do you think it could be valves? Would that account for such low compression?
Most don't do compression checks on newer four strokes because they have automatic decompression mechanisms. Could be why u are seeing low compression on the gauge.
sgrimmxdad
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sgrimmxdad 11/29/2015 6:22am
11/29/2015 6:22am Edited Date/Time 11/29/2015 6:24am
http://www.vitalmx.com/forums/Race-Shop,42/2015-YZ250F-PROBLEMS,1285291

Read my thread. After THOUSANDS of dollars wasted chasing this problem mine seems to have been the TPS sensor. Yamaha made a new one to replace the original part. The old and new part number is in my thread. Good luck! Yamaha should recall the damn things. We bought a new 16, still race prepping it. Hoping not the same problems! Identical problem, seen it on SEVERAL 15's!
Jaybird67k
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Jaybird67k 12/2/2015 5:15pm
12/2/2015 5:15pm
tyler.hettick wrote:
If it was running and then died do you think it could be valves? Would that account for such low compression?
slackinoff wrote:
Most don't do compression checks on newer four strokes because they have automatic decompression mechanisms. Could be why u are seeing low compression on the gauge.
Like he said. A compression check on a auto decompression bike will read lower than normal because one exhaust valve is being held open while kicking until it fires and the rpm increases there fore releasing the exhaust valve so it can seat.
I am having a similar problem with a 2015 YZ 250F that just started bogging and popping with 20 hours on it. It fires up fine but bogs as soon as throttle is applied. I dumped the fuel to make sure no water. Then the plug. No dice.

So as soon as I got home I did a leak down test and had 10% so now I know it's not a mechanical issue. It rules out timing errors, valve issues, ring issues, piston to cylinder clearance issues and many more mechanical things so now it's on to what the actual problem is.
ALWAYS, AND I MEAN ALWAYS DO A LEAK DOWN TEST FIRST !!!

I have chased my tail on FI bikes for months only to finally do a leak down and find a stuck ring or valve not closing with 85% leak by.

I check my compression even though it doesn't mean much with a auto de compressor and had 130lbs with the exhaust valve slightly open with the auto de compressor.

Jason

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