01 KX250 sporadic throttle changes

Last time I was out riding the throttle started sporadically changing.  The throttle also jumped to about 50% and stayed there a couple times.  I tried the kill switch wile this was happening,,, nothing, Kept screaming.  Any other time the kill switch works fine.  Only time it doesn't work is when the engine jumps to 50% throttle by itself.
Any ideas?  

I'm not sure but maybe its something electrical, im not sure how the KX's work but someone here should know. but the fact that it stays there and the killswitch doesnt work, may be an indication that its not a carb issue, but electrical, but maybe it can be both.

And welcome to the board!  
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2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

Thanks Force,
My first thoughts were a stuck slider or cable.  Maybe an air leak.
But with the kill switch not working, I'm thinking electrical too.
Its really weird though.  How could it be jumping up to 50% throttle and staying there by itself?  With no throttle input at all?  

No prob dirt eater!
Yeah weird is the word to describe this!
Yeah a stuck slider is mostly the problem with this, but yeah as you said, jumping to 1/2 throttle and killswitch no worky, i think give the carb a good clean, and see what it does, maybe the theres something wrong in the carb and electrical, because jumping to 1/2 throttle by itself, and then the killswitch not working, i thought it could be the TPS(throttle positioning sensor) i dont know if the KX's have them.

But we will get to the bottem of this! someone else will also reply here! maybe they had the same problem!  
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2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

I believe it may have a TPS.  There is two sets of wires going to the top of the carb.  No idea what they do right now.  

Found this on the web, sounds like it could be to blame.

Symptoms of a Defective Throttle Position Sensor:

   * Bucking and jerking
   * Idle surging
   * Sudden stalling
   * Hesitation while trying to accelerate
   * Sudden surge speed  

hey guys the reason why the kill switch is no working is becuse, the ammount of power the kill switch gives off is not enough to shut a bike off at that high of idel, lets just say it dose not have the juice power. sencond of all i think your slide is stuck this happened on my old bike and it would rev so loud, one time  had to unplug all the electrical wires before it  blew.  but ya if you have TPS this could be a short or dirty connection wire allowing it to not function properly, tell me any more info you have and iwill try to help.  
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Autismspeaks.org   check it out
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life in the fast rut!!!!
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my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
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Home: SO CAL

Yeah makes sense Alex! but the thing is.. how can the slide get stuck if no throttle is given? it must be something electrical, but it also wouldnt hurt to check the reeds aswell, and the TPS is like a thing lol that has an arm that pushes down on the slide, it may be the problem! but DON'T remove the TPS if you are not exactly sure that its the problem! and yeah give your wires a good clean, disconect them and see if they are dirty, or if it may have been cut in some way.  
<><><><><><><><><><><><>

2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

May seem odd but I would check the kips power valve on it. I think it has Kips right? My friends had  KDX 200 that had a problem with his idle. It would rev high and stick open when he was riding, very dangerous. Turned out that the rod was not connected the the valve and I beleive that was the problem with his bike? Once i hooked it up it solved his idle problem. He also had a bad water pump seal and lost all his fluid and it super heated the engine and cause other problems but I beleive his idle problem came from the power valve. Just a thought?  
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"These are the things that condition the man, seldom shown the ways to understand"

Thanks for all your input fellas.
I recently had the engine rebuilt.  It was running great for the first 5 trips out.  I did wash it at home the night before it started having these issues.  That day, I made it up to the top of a local mountain with no problems.  I let the bike cool down for about 30min.  As soon as I got it going after taking the break, the idle was off.  Wanted to die.  I adjusted the idle to compensate for the change before I started heading back down.  The engine started giving little bursts of throttle here and there with no throttle input.  About half way down the mountain I went over a small jump. About two seconds after I landed, the engine all of a sudden jumped to around 50% throttle with no input.  It would stay right at whatever RPM's it was at until I would kill it manually.
I hope this info helps.  

dirteater81:
Thanks for all your input fellas.
I recently had the engine rebuilt.  It was running great for the first 5 trips out.  I did wash it at home the night before it started having these issues.  That day, I made it up to the top of a local mountain with no problems.  I let the bike cool down for about 30min.  As soon as I got it going after taking the break, the idle was off.  Wanted to die.  I adjusted the idle to compensate for the change before I started heading back down.  The engine started giving little bursts of throttle here and there with no throttle input.  About half way down the mountain I went over a small jump. About two seconds after I landed, the engine all of a sudden jumped to around 50% throttle with no input.  It would stay right at whatever RPM's it was at until I would kill it manually.
I hope this info helps.

now from that as barry [riding the rockies] stated now that sounds more like a valve sticking, sounds like the same problem pat had with his power valve, so maybe check your valves next maybe one is messed up or gunked up?? who knows, thanks for the more INFO.  
--------------------
Autismspeaks.org   check it out
--------------------
life in the fast rut!!!!
--------------------
my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
--------------------
Home: SO CAL

Waiting for the weather to clear up, but I think i fixed it.  If it turns out it was just a sticky throttle, I'm going to be a little ashamed.  It really threw me off when the kill switch wouldn't work.  Thought it had to be electrical.  Checked the TPS the other night.  Closed 4.3kOhms - 1.4kOhms Open. Didn't miss anything in between.  

Finally was able to take it out for a test run.  Everything appears to be working fine.  

Ok cool eater! glad it worked out!  
<><><><><><><><><><><><>

2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

Well, looks like that wasn't the problem. Do you think it could be because of the rich oil mix?