Engine surge/runaway?

Mustyeddie

New member
Edit: The problem has since been resolved, as there was a massive crack in my carb-reed boot. I feel quite silly now that I have found the (minimally small) issue… but the bike runs fantastic and is literally faster than a buddies 2024 250 XC-W…

2000 Gas Gas EC250 with unknown hours and good compression. I’ve owned since March of this year and put 25+ hours minimum on the bike with very minimal issues.

About three weeks ago, I realized the bike was lacking a big, as it was fouling plugs more often and lack of power in higher RPMs (where the meat of the power should be) unless I was in 4th, 5th, or 6th gear. I took apart the carb and cleaned it well, reinstalled the carb and the bike ran better. I switched to 50:1 (after inquiring at the local Rieji dealership about proper mixing) from 40:1 (what the previous owner had told me he was running) and it seemed to wake the bike up quite a bit. During the test ride, I neglected to properly set my chain tension with the new chain I installed while the bike was sitting. The chain popped off the rear sprocket and destroyed my clutch slave cylinder housing.

It took me about three weeks to source a new replacement slave cylinder, but I was able to track one down and install it with no problems. Bled the clutch out and went for a test ride, the bike began running weirdly, but I was able to limp the bike home to my garage. The bike now has a sort of “double blip” to the idle and will run away if given the slightest throttle input. I have had to pull the boot quite a few times now to get the bike to shut off while testing different carb settings and etcetera. I adjusted the throttle cable to an acceptable tolerance, removed, cleaned, adjusted, and then replaced the carb with an OEM Keihin pwk38.

I am unsure of what this issue could be, and am weary of starting the bike any further due to the constant running away (5+ times now). Any help would be greatly appreciated, thanks!
 

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If you can kill the bike with the kill switch it is likely you have an air leak somewhere. Stator side main seal, air boot, etc.

If you cannot kill the bike with the kill switch, it is caused by pre-ignition in the combustion chamber.
 
If you can kill the bike with the kill switch it is likely you have an air leak somewhere. Stator side main seal, air boot, etc.

If you cannot kill the bike with the kill switch, it is caused by pre-ignition in the combustion chamber.
Thanks for the info, definitely helped me track down the leak!
 
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