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yz250 is Surging?

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I'm kinda stumped

 

The bike starts up fine and idles no problem. After riding it for about 10 or so minutes it starts to get these idle surges, like someone is reving the throttle every 1 to 3 seconds. Also sometimes the bike will just rev full throttle for no apparent reason and the kill switch will not function. Other times you come to a stop and everything is normal so i'm guessing it is something with electrical based off it makes no sense lol. I was searching on here and ran across the throttle position control sensor, i just check it and it a little out of spec 3.68 but i dont know if that would cause all those problems either. 

 

if you got any ideas let me know

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I'm no expert but could the jetting be off?

Yup, but if the bike was running good before and then suddenly changed, generally something else is wrong....

Sounds like all the common symptoms of a airleak to me though...

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Sounds like an air leak to me as well... easy way to rule out an air leak (since you have surging it is probably a decent leak) is to start turning in the AS and see if the surging persists or at least doesn't improve you can pretty much guarantee that you have an air leak. 

Edited by BDubb106

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So i did the top down tester. I was losing a ton of PSI from reed gasket, so i replaced it. It still leaked a little but i think it was from not being able to get a good seal around the elbow of the tester. When i pumped it up i could hear it from the intake and i couldnt see any bubbles from anywhere else. I also took apart and cleaned the carb as well as reseating my exhaust pipe and sealing the connection from the expansion chamber to the silencer.

 

 

I ran it a little and it definitely ran alot better but had a hint of surging still ( normally it runs fine for a while then starts after running it while) I need to take it out this weekend to see if it still does it, I cant really ride it the neighborhood. Also i put all my carb settings back to stock so i'll need to play with that.

 

If that doesn't fix it i guess i'll try the crank seal.

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I took it out a couple weekends ago and it was pretty bad. I just haven't found the time yet to dig into it more. i'll take off the slator cover and see if there is premix in there.

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My bike was surging when I went to the beach, but was great up in the mountains. I upped both jets 2 sizes and turned my air screw in a bit. Surging at the beach was solved. So definitely try adjusting the carb.

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It can also be head gasket. When the rings split it tends to shoot the jetting right out the window once the motor heats up. Had this issue on my 265. Ran brilliant from cold but once warm coming into corners on a clased throttle it would literally surge forward like the throttle had been blipped. spent ages pointlessly chasing jetting. Changed split inner o-ring and it ran spot on.

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Sounds slightly lean. Check jetting first before you spend time and money on other things.

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Case leak. Test it, or just replace the seals.

Intake leak. Test it or buy a new manifold.

Head leak. Replace the o-ring.

Head perimeter hot spots due to carbon build up (caused by rich jetting needed for wide squish). What is your clearance? So easy to check it.

Damaged reeds. Just another guess.

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