YZ250F (2018) Starting Issue

mnoble0902
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mnoble0902
Note: I posted this in the Tech Forum as well.

Hello,

I was riding on Saturday and suddenly my engine quit and I couldn't get the bike restarted. This happened during my first lap. As I was trying to get it started, I noticed pressure building in the kick starter. It got to the point where it wouldn't move. Someone looked at it with me. He put the bike in gear and turned the rear tire. This released the pressure and the bike started normally. It sounded fine at idle and when I turned the throttle. Also, no signs of power loss or bogging sound. I went back out on the track and the same thing happened again. I can push the bike without issue, so I don't think the transmission has seized. Spinning the tire on the stand, everything sounds normal.

When I started the bike for the first time on Saturday, it started on the third kick like it has since I bought it. It ran fine and didn't show any signs of quitting. Any idea what may be going on? I'm really hoping it is not valve or piston related. It doesn't seem like it would be if I was able to get the bike restarted and it runs like it always has.

One thing I should mention is I washed the bike Thursday before riding. Afterwards, I started it, but forgot to remove the exhaust plug...doh! It started, but for less than 5 seconds. I then removed the plug. When I removed the plug, I heard air or something come out of the exhaust. Could this be related to my problem?
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Talisker
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Talisker 12/3/2019 8:28am
12/3/2019 8:28am Edited Date/Time 12/3/2019 8:30am
Has the fuel tank been removed recently? Make sure the fuel line is not pinched or twisted. Sounds silly, but it’s very easy to do.
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mnoble0902
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mnoble0902 12/3/2019 9:37am
12/3/2019 9:37am
mattyhamz2 wrote:
Check your fuel filter.
Thanks. I'll check that. Would an issue with the fuel filter cause the kick starter to not move though?
mnoble0902
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mnoble0902 12/3/2019 9:38am
12/3/2019 9:38am
Talisker wrote:
Has the fuel tank been removed recently? Make sure the fuel line is not pinched or twisted. Sounds silly, but it’s very easy to do.
I have not removed the fuel tank, but I'll still check the fuel line. Thank you.

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mark_swart
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mark_swart 12/3/2019 9:38am
12/3/2019 9:38am
That sounds weird. I have a 17 and had problems once after some moisture got into the electronics, I disconnected and cleaned them all and it has been fine since. My symptoms were totally different. Maybe a problem with the fuel cap or vent, if none of the suggestions above make a difference.
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SCAM124
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SCAM124 12/3/2019 10:02am
12/3/2019 10:02am
Your kickstarter getting tighter and tighter as you kick makes em think you are getting hydro-locked or vapor-locked but the description of how it happens isn't consistent with that. My Homer-brain is telling me that I'd be looking closely at your cam chain tensioner? I dunno...weird stuff.
4
mnoble0902
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mnoble0902 12/3/2019 10:40am
12/3/2019 10:40am
Thank you for your responses to far. This is very weird. I'm going to look at everything that you all have suggested so far, but it is strange how these things could affect the kick starter. It's probably because I don't understand something.
mattyhamz2 12/3/2019 10:50am
12/3/2019 10:50am
mnoble0902 wrote:
Thank you for your responses to far. This is very weird. I'm going to look at everything that you all have suggested so far, but it...
Thank you for your responses to far. This is very weird. I'm going to look at everything that you all have suggested so far, but it is strange how these things could affect the kick starter. It's probably because I don't understand something.
Check the easiest things first. Fuel line, fuel filter and other things like that before tearing into the motor.
mnoble0902
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mnoble0902 12/3/2019 11:02am
12/3/2019 11:02am
mnoble0902 wrote:
Thank you for your responses to far. This is very weird. I'm going to look at everything that you all have suggested so far, but it...
Thank you for your responses to far. This is very weird. I'm going to look at everything that you all have suggested so far, but it is strange how these things could affect the kick starter. It's probably because I don't understand something.
mattyhamz2 wrote:
Check the easiest things first. Fuel line, fuel filter and other things like that before tearing into the motor.
I really hope it is something simple. I really don't see how it would be something in the motor. I'm definitely on the newer side when discussing rider skill level and I haven't even come close to reving the bike out.
resetjet
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resetjet 12/3/2019 11:03am
12/3/2019 11:03am
Only thing i come up with is a sticky exhaust valve.
Of course it could be malfuntion of kick start mechanism. Did it just quit riding or did you stall/crash the bike.
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mnoble0902
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mnoble0902 12/3/2019 11:10am
12/3/2019 11:10am
resetjet wrote:
Only thing i come up with is a sticky exhaust valve. Of course it could be malfuntion of kick start mechanism. Did it just quit riding...
Only thing i come up with is a sticky exhaust valve.
Of course it could be malfuntion of kick start mechanism. Did it just quit riding or did you stall/crash the bike.
I was coming down a straight into a corner. At the exit of the corner, I rolled the throttle on hard and nothing... The bike just quit.
vitalriderCrf 12/3/2019 1:52pm
12/3/2019 1:52pm
I would check your cam chain, tensioner and guides like Homer suggested. Maybe your bike jumped out of timing, my buddy’s 2012 KX450 did that. Good luck
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resetjet
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resetjet 12/3/2019 1:57pm
12/3/2019 1:57pm
I say something got stuck and by turning the rear wheel in gear you unstuck it. Probably more then one issue. Something loose or out of place somewhere. Take top end apart and check everything. I think you will find the answer. Make sure exhaust is clear too. Its only a blockage in the exhaust circuit that will cause it to build pressure, or it was the kickstart mechanism making you think it was “building pressure”
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ctbale
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ctbale 12/3/2019 3:09pm
12/3/2019 3:09pm Edited Date/Time 12/3/2019 3:22pm
The fact it wouldnt kick over says hydo lock, but that wouldnt happen after an unwanted shutdown.
then by turning the rear wheel (in gear?) freeing it up points to kick start mechanism? Dont think stuck valve or skipping a tooth cuz those dont fix themselves and crank/piston should still move. Blocked exhaust wouldnt cause a stuck kicker either. Maybe piston seized, then when it cooled down it came unstuck? Interesting set of symptoms for sure. Is there oil in the engine?
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mnoble0902
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mnoble0902 12/4/2019 5:20am
12/4/2019 5:20am Edited Date/Time 12/4/2019 7:09am
Thank you for the new suggestions. I talked to the dealer I bought the bike from and he said it could be vapor lock. I'm also thinking it could be hydro lock like a few have suggested because I did wash the bike a couple days before. Perhaps too much water got in places it shouldn't be? I really hope it is not a stuck valve or seized piston. Ugh.

The Yamaha dealer said to bring it in and they will run a couple tests on it.

This has become quite the puzzle to figure out.
mnoble0902
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mnoble0902 12/4/2019 5:21am
12/4/2019 5:21am
ctbale wrote:
The fact it wouldnt kick over says hydo lock, but that wouldnt happen after an unwanted shutdown. then by turning the rear wheel (in gear?) freeing...
The fact it wouldnt kick over says hydo lock, but that wouldnt happen after an unwanted shutdown.
then by turning the rear wheel (in gear?) freeing it up points to kick start mechanism? Dont think stuck valve or skipping a tooth cuz those dont fix themselves and crank/piston should still move. Blocked exhaust wouldnt cause a stuck kicker either. Maybe piston seized, then when it cooled down it came unstuck? Interesting set of symptoms for sure. Is there oil in the engine?
There is definitely oil in the bike. I just changed it not too long ago.

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