I can’t figure this out and need help. My buddy has a 01 KTM 125sx that won’t rev out unless the gas is turned off.
I’ve already checked the power valve, electrical, new plug, clean air filter, muffler packing, cleaned the carb till it was spotless, set the float height, checked the reeds, and pulled the ec to check the condition of the cylinder. The cylinder had minor scoring, same with the piston, but not enough to consider a top end rebuild.
He’s had the bike for years, and absolutely nothing on it has changed. He hasn’t moved, hasn’t messed with the carb, nada. Then he ran 110 octane fuel in it, which it ran fantastic with for the first tank, and now won’t run right unless the fuel is off.
The best way to describe how it acts, is it starts to rev out, then cuts, then starts to rev out, cuts, etc. However, when the fuel is turned off it runs perfectly fine, revs out all the way, crisp and clean.
I posted a short on YouTube to try and get some help there, I’ll post the link here:
https://youtube.com/shorts/L8urKy0afJo?si=c2i6wX-Y2MpnpxNw
Any help would be greatly appreciated!
Wierd. I know you said you clean the carb, but did you specifically also clean the seat that the float needle goes into?
The first time I cleaned the carb it was full of gunk. Valve seat, main and pilot had debris in them. I pulled them all and cleaned them out/off. I wouldn’t be surprised if the rubber on the float needle itself is just hardened to the point it doesn’t seal anymore, considering it’s 20+ years old. It didn’t show any signs of corrosion or wear, but it could be microscopic.
Last night I double checked the float height and set it lower to see if maybe it’s not putting enough force on the needle to stop the flow of incoming fuel. I’ll run it today and see if that fixes it.
Sounds like float needle that doesnt seal properly anymore indeed. Take of bottom of the carb, see if pushing the float to the correct height properly shuts off the fuel supply. Would order a new one anyway, or go with carb revision kit
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Problem lies in the float
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