2005 YZ250 revving on idle (runaway)

k-bull98
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k-bull98
I just purchased a 2005 yz250 and took it out for the first time today. The bike was fine for the first couple of moto's on the track. On the fourth moto I started to notice the bike revving up as I grabbed the clutch in the corners. I went back to where I was parked and by the time I got there each time I pulled in the clutch or went into neutral the bike would start to rev up with no gas.

From my research, it seems like it may be a crank seal leaking. Is it worth trying to look at the throttle cable or carb? I did notice there wasn't much slack at all in the throttle but it was like that from when I bought it.

Notes: After the first moto I was able to almost get the tank to empty and then filled the tank 1/2 full with recently purchased 93 pump gas with Belray H1-R oil at ~30:1 ratio (maybe slightly richer).
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TrailDigger 11/6/2017 6:05am
11/6/2017 6:05am Edited Date/Time 11/6/2017 6:05am
You can check the airboot and around the reed cage for cracks or anywhere it might be sucking air, leading to a lean issue.
F150Motocrosser 11/6/2017 6:42am
11/6/2017 6:42am
Spray a little ether or starting fluid around anywhere that you suspect an air leak.. If it results in the RPMs surging, there ya go.

Also, have a buddy move the bars form totally left to totally right a few times. Keep your eye on where the throttle cable comes out of the top of the carb, see if you can tell it's being stressed or pulled. Your throttle cable routing could be wrong. Sounds possible since you noticed issues in the corners..
k-bull98
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k-bull98 11/6/2017 8:48am
11/6/2017 8:48am
F150Motocrosser wrote:
Spray a little ether or starting fluid around anywhere that you suspect an air leak.. If it results in the RPMs surging, there ya go. Also...
Spray a little ether or starting fluid around anywhere that you suspect an air leak.. If it results in the RPMs surging, there ya go.

Also, have a buddy move the bars form totally left to totally right a few times. Keep your eye on where the throttle cable comes out of the top of the carb, see if you can tell it's being stressed or pulled. Your throttle cable routing could be wrong. Sounds possible since you noticed issues in the corners..
Thanks for the tips. I don't think it's the throttle cable as it did it as well when it was on the stand. But I'll still take a look at it this afternoon.


Can anybody recommend any good shops or mechanics in the DFW area? Preferably closer to Fort Worth.

(Just recently moved and no longer have the tools to work on anything once I split the cases)

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