2013 KX250F Cutting out

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9/23/2018 7:38 PM

On my 2013 KX250F the bike all the sudden wants to cut in and out like it is starving for fuel. Problem started after I crashed awhile back and had to replace just the subframe and exhaust but nothing else. After I put the bike back together this is when I was having problems. Started off whenever I was half way through a moto the bike would just start missing like when I was at a steady half throttle and seemed like when the bike was hot the problem would occur. The bike still starts right up every time. After I put a couple more rides on it the problem got worse and now cuts in and out when 0 to half throttle right off when I warm the bike up. Even when the bike is warming up I can tell it's not right. I have checked for codes and the bike is code free. Went through throttle body and had injectors cleaned, new plug, and checked valve clearances, checked fuel pump and still nothing. If anyone can help I would appreciate some feedback! Need this bike back and running asap. Thanks!

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9/23/2018 9:55 PM

First thing it sounds like you need to do is get a spark light and see if youre getting consistent spark when its hot. A lot of the times ignition parts will get fussy when they heat up.

This issue could literally be 100 diff things, so lets start simple first.

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9/24/2018 11:16 AM

More than likely, your throttle position sensor (TPS) is out of whack. Posts like this, regarding that specific bike, pop up fairly often here and on thumper talk. The process for adjusting the TPS back into proper spec is fairly vague and theres not a whole ton of information about it online. It's happened to my 2015 KX250F after a crash, I assumed the TPS got knocked and became out of spec. Basically, at closed throttle you should get a certain voltage reading and theres a specific set of value range it should fall within. As you twist the throttle, the voltage reading should go up and peak at wide open throttle within a specific voltage value range. When the TPS gets hit or twists, the values will change. In fact, thats exactly how you make adjustments to the TPS, by altering the position of the TPS itself.

You'll need to do some research on youtube and check out TPStool.com.

Another common suspect would be a dirty or clogged fuel pump filter. But it sounds like you've already inspected that.

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9/26/2018 4:21 PM

You mentioned the problem came about after replacing subframe and exhaust. When you took off the subframe, did you leave the airbox/airboot in place? If you removed it, ensure you have the air temp sensor plug and the upstream injector plug connected well. Doesn’t hurt to clean the plugs with a quick evaporating solvent and then put some dielectric grease on the terminals. Also ensure that the fuel hose/pipe going to the injector is fully seated and clipped.

By the way, my paint marks on the tps looked correct too when it was cutting out. the TPS is so sensitive to movements in my experience.

Does the hole shot button on the handlebars display any codes/lights while the bike is running? Maybe an audible video that shows the symptoms will helpZ

Is it cutting out to the point where it’s nearly un-rideable? Not like a fuel rich hesitation/burble, more like the bike has run out of fuel?

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9/26/2018 7:28 PM

pCp 252 wrote:

You mentioned the problem came about after replacing subframe and exhaust. When you took off the subframe, did you leave the ...more

I just want to add to your point about the tps.. once you get your tps tool, youll be able to see you can literally apply pressure with your finger to the sensor and change the voltage value. Using the paint isnt really a good indicator. Those sensors are super sensitive.

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9/26/2018 7:30 PM
Edited Date/Time: 9/26/2018 7:32 PM

pCp 252 wrote:

You mentioned the problem came about after replacing subframe and exhaust. When you took off the subframe, did you leave the ...more

Yes, I did have air box removed and cleaned and put the connectors back on and the fuel hose is sealed correctly. The tool for TPS should be here Saturday and I'll get the TPS dialed in if it isn't. The bike has no codes. It is cutting out like it isn't getting fuel, kinda like running lean and is not really un-rideable. I only ride it when testing stuff out for a short period of time. Maybe I can get a video up when starting it and riding this weekend.

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10/1/2018 1:19 PM

UPDATE: I checked my TPS and it is reading perfect. Thinking my ECU is the problem? Thoughts??

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10/1/2018 2:16 PM
Edited Date/Time: 10/1/2018 2:17 PM

Have you cleaned the fuel injector?
Have you checked the fuel pump and filter?

Paw Paw

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10/6/2018 6:05 PM

I have went through the entire bike and switched stuff from another running KX250F besides the ECU. Only thing I can think of is it has to be that unless I'm missing something. If I find problem out I will be letting everyone know. Thanks.

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10/6/2018 6:32 PM

Did you literally switch everything?

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10/9/2018 12:24 PM

kb228 wrote:

Did you literally switch everything?

Yes, besides wiring harness and ECU. Could it be the stator? To me it is a fuel problem the plug is like white after I ride it for the short amount of time I ride it and the bike sometimes pops loud on deceleration and it never has done this until the problem started. Timing I will triple check also.

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10/9/2018 1:25 PM

I doubt timing is the issue. In my experience the KXs wont run at all if its off by 1 tooth.

Something on your bike is telling it to run lean. You got air sensors, TPS, coolant temp sensor, or an air leak making it run that way.

Does adjusting your TPS voltage to the richest setting make a difference?

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10/10/2018 12:36 PM

kb228 wrote:

I doubt timing is the issue. In my experience the KXs wont run at all if its off by 1 tooth.

Something on your bike is ...more

Let me try that tonight, I'll let you know

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10/10/2018 3:06 PM

kb228 wrote:

I doubt timing is the issue. In my experience the KXs wont run at all if its off by 1 tooth.

Something on your bike is ...more

Blake_Guldi wrote:

Let me try that tonight, I'll let you know

So saw oil leaking a little from oil filter cap, o-ring is shot. Read in manual just today, if air is getting in from oil cap or filter cap it can cause issues with the fuel mixture and so on. I'm getting a new o-ring ordered and will go from there. Thoughts? Do you think this can be it??

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10/10/2018 4:47 PM

kb228 wrote:

I doubt timing is the issue. In my experience the KXs wont run at all if its off by 1 tooth.

Something on your bike is ...more

Blake_Guldi wrote:

Let me try that tonight, I'll let you know

Blake_Guldi wrote:

So saw oil leaking a little from oil filter cap, o-ring is shot. Read in manual just today, if air is getting in from oil cap ...more

I guess it makes sense. Air gets into the crank shaft area and above the piston it could. I havent seen that in my kx250f or kx450f manuals. Same time tho the bikes have vents coming off the bottom end anyways so i dont know why it would make much of a difference.

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10/10/2018 5:16 PM
Edited Date/Time: 10/13/2018 7:44 AM

kb228 wrote:

I guess it makes sense. Air gets into the crank shaft area and above the piston it could. I havent seen that in my kx250f or ...more

Right that's what I thought. I'll give it a try and let you know. It's in the manual under troubleshooting for the fuel section.

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10/13/2018 11:34 AM

Blake_Guldi wrote:

So saw oil leaking a little from oil filter cap, o-ring is shot. Read in manual just today, if air is getting in from oil cap ...more

kb228 wrote:

I guess it makes sense. Air gets into the crank shaft area and above the piston it could. I havent seen that in my kx250f or ...more

Blake_Guldi wrote:

Right that's what I thought. I'll give it a try and let you know. It's in the manual under troubleshooting for the fuel ...more

The o-ring is just a coincidence I fixed that and bike still cuts in and out. I ran it today, it is a lot colder out and it really didn't cut in and out all that much but it is still there. Problem is definitely worse when hot I'm finding out. I was told it maybe my stator?

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10/13/2018 1:55 PM

If its spark related, start at the spark plug, then cap, then coil, then rectifier, then stator, then ecu

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10/21/2018 6:21 PM

Replaced the stator and rode this weekend. The bike did not cut out that I noticed. Hopefully it stays good. If not I will be posting back on this. Thank You.

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