Posts: 100
Joined: 1/31/2018
Location: Rock Creek, OH USA
Just bought a brand new 250sx. get it home and i hear this knocking while at idle like detonation, pinging, what have you. i take it to the dealer and they said yes it was detonation put richer jets in it. i do that and it is still doing it but not as bad. running motorex at 60:1 and vp 110. any advice guys. thanks so much
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Edited Date/Time:
much ty. How to spot a paid forum poster/artificial forum traffic producer (see list of actions/phrases below):
Copius pattern amounts of phrases like “Anyone have”..., “Anybody know?”.... and their variations.
Thoughts?
Any help is appreciated!
Thanks in advance!
Posts: 100
Joined: 1/31/2018
Location: Rock Creek, OH USA
Posts: 923
Joined: 12/19/2009
Location: Westfield, MA USA
Do some research here and over on KTM talk, jetting issues on this machine are well documented. The shortest and easiest way to happiness will be, get cylinder head cut to close up the squish, JD jet kit, V Force reeds.
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Location: League City, TX USA
I had a JD jet kit in my 13 250sx and it was night and day difference. Never fooled with jetting after that.
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Location: The Woodlands, TX USA
Thread that has in-depth jetting on your bike.
https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/17-TC250-Jetting-Help,1329212
Why are you running C110? It's unleaded, switch over to C12 as its leaded and will help some performance wise as well.
2018 KTM 250sx
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Posts: 100
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Location: Rock Creek, OH USA
AJ565 wrote:
Thread that has in-depth jetting on your bike.
https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/17-TC250-Jetting-Help,1329212
Why are you running C110? It's unleaded, switch over to C12 as its leaded and will help some performance wise as well.
that’s what the dealer told me to run. here is the plug the bike runs fine except for that damn knocking noise. 
Posts: 123
Joined: 2/9/2011
Location: novato, CA USA
My 17 TC250 makes the same noise. Only at idle. From my research I found that it is just a low rpm gear slap from the counterbalancer. If you take off the L side engine cover you can wiggle the counterbalancer back and forth and it makes a small clunking noise. I believe that is where the noise is coming from.
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Location: Rock Creek, OH USA
paddyB745 wrote:
My 17 TC250 makes the same noise. Only at idle. From my research I found that it is just a low rpm gear slap from the counterbalancer. If you take off the L side engine cover you can wiggle the counterbalancer back and forth and it makes a small clunking noise. I believe that is where the noise is coming from.
yeah like if you let off the gas as it is simmering down you’ll hear a “knock knock”
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Location: The Woodlands, TX USA
I was wrong about the VP110, I was thinking of C10 as that one is unleaded. The dealer I normally get fuel from is out of C12 so I'm going to get some VP110 and run it this weekend. It's really close to C12 so I'll report back if I notice any performance difference or noises.
2018 KTM 250sx
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my buddy's '18 250sx knocks as well. he is running JD kit. trying to figure out what it is.
my '18 300xc does not knock
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mine made the same noise. I had a 16 250sx with the jd kit. Does it get quieter when you pull the clutch in
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