2016 KTM 125SX acting sluggish at times.

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7/3/2018 10:25 AM

Didn't ride for a good two months due to a small injury, my last ride on the bike was a brutal mud hare scramble. Two months later I finally get to ride again, bike revs out good, get onto the track and open it up and doesn't feel like it wants to pull, keep riding thinking maybe it just needs cleared out, no luck. Go to pits, New plug, go on track, does the same thing but clears itself up about two laps later and runs fine all night.

Week and a half later go ride again, Do three 20 min motos and runs great, park it for an hour for a lunch and track groom break. Take the bike off the stand and start it and it does it again, this time in neutral it revs noticeably slower, and is still sluggish as hell, doesn't pull in any gear again. Take it to the track and try to ride it out like last time. 5 laps and it doesn't work, change to a new plug, doesn't work, same thing.

Anyone have any ideas, my jetting is spot on, i'm running 110 race fuel, PC mod motor, Clean airfilter, 32:1 with Castor 927. Never had this problem with this bike and have had it for a while now.


Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

7/3/2018 10:42 AM

Check that the powervalves are opening and shuttling properly. Take off the left powervalve cover and start the bike. Make sure it's not stuck closed or stuck open. If that checks out, clean the can float bowl and makes sure there is no debris floating around since the last race was a mudder. Check all connections and electrical plugs as well. Take off the stator cove and make sure everything looks ok. Obviously you put fresh gas in and the problem seems intermittent which is weird. Good luck and keep us posted.


7/3/2018 11:53 AM

Sounds like powervalve getting stuck. It's a known problem with some of the 16-18 125/150s.


7/4/2018 8:30 AM

Also have a look at the reeds


7/4/2018 11:22 AM

I didn't have a problem with my OEM arms, but I put in these F1 power valve arms while I did my whole rebuild. I also had the ISF polished with my tranny parts. The curve on them is smoother than the OEM design.



7/5/2018 5:01 AM

Not trying to scare you but same thing happened to my 16 250sx. I did a real muddy/dusty ride and the bike ended up sucking in a bunch of dust and dirt. Only thing I can think of is that I didn't seat the air filter properly. Rode fine for a while but started to bog and wouldn't rev out all the time. But sometimes is it was fine. Pulled the top end apart and it was fucked.


7/5/2018 1:12 PM

More than likely it's the powervalve.

Take it apart and clean and polish everything!

Also water can leak into the PV and rust the bearing that lets the barrel move.

Good Luck!


7/6/2018 5:50 AM

Check the ground on the coil. Make sure its clean, little sand paper on the frame and coil, bolt it back down.


7/12/2018 7:13 AM

Dad was working on the bike while i'm away and told me the "keeper" fell out of the power valve. Gonna put some loctite on it and get some riding in this weekend. Thanks for all the help guys!


Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

7/12/2018 8:25 AM

Good to hear! Have fun!