2017 250 Sx-F, long story short, started the bike without a muffler, it started and then popped and died. I tired starting it again and after a few seconds of turning over it would start but then blubber out and die and a normal idle, it would sorta stay alive if you gave it a tiny bit of throttle but any rev and it would die. Have the whole head pulled apart right now. No clear signs of wear on the valves, just a little dirty from the carbon but i think that’s normal. Valve seals don’t look terrible, but i notice the holes look a little bigger and more warn out then some extra new ones i have which i will switch out but idk if that’s causing the whole problem. Spark plug looks pretty dark and burnt at the tip. Any ideas on what i should look into?
Your 2017 KTM 250 SX-F stalling issue after running it briefly without a muffler could be due to a few things. Start with a compression and leakdown test to rule out valve sealing issues, especially since your valve seals look worn. Double-check cam timing, as even one tooth off can cause these symptoms. A fouled spark plug suggests it may be running rich or not igniting properly—check for strong spark and test the coil. Also inspect the fuel injector, TPS calibration, and ensure there are no air leaks. Once the head’s back together, verify everything's sealed and timed right.
Interesting that ChatGPT didn’t have any concern of bad piston rings
I thought the same thing
Could be as simple as a fouled plug.
The Shop
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Luxon 4-Post Bar Mounts
$189.95 - $239.95
Free shipping: VITALMX
Possibly but dosent really explain the blue smoke and smell of burnt oil
You didn’t hurt anything starting it without a muffler whatever issue you’re having you would have had regardless.
Welp it sure made a big pop and then had problems
That could be unburned fuel, it would be in a rich scenario with less than optimal spark.
Post a reply to: Accidentally started with no Muffler