I have a 2021 Husky Tc250 with just shy of 50 hours. Recently while ridng at my local track, I landed a jump pretty hard and after that the power valve will barely open. The bike has a little bit of low end power but after that it has nothing. Also it sounds different as well. I have checked all the components of the power valve as well as the linkage and everything is workings as it should be. I rejetted my carb for the elevation(7220 ft), I just recently moved to wyoming from chicago so about a 6500 ft gain. I also took off the cylinder and cleaned all the carbon off the piston and my cylinder looks brand new. I have disconnected, cleaned, and greased a lot of the electrical connections. I also checked the reeds and they look fine. I think it is important to note that while the bike is in neutral, it will rev out and the powervalve opens, it still does sound a little weird. When I ride it down the road, i've had the left power valve cover off and I can watch it stay mostly closed. Some background about the bike is I bought it new, i'm an intermediate rider at best, at least half of the 50 hours on the bike are trail hours. I do very regular maintenance, air filter uasually ever 1-2 rides and oil every 5-10 hours. Also I forgot to add above that the bike starts and idles perfectly fine. If anyone has information on this it would be greatly apreciated as I would prefer to not have to drive a ways to get to the nearest KTM dealer. Thanks
Has the power valve adjusting screw backed out?
I havent touched that at all, so its where it came stock I believe.
Broken spring?
Nope I checked the spring and tried the other ones too
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Unless it's the governor, I've got nothing!
Is the mapping switch working? It wouldn't affect the power valve, but would affect ignition timing.
Did you remove the right side cylinder cover and inspect all the linkage in there? It sounds like something with the governor, linkage or in the cylinder itself has gone out of whack.
Would check that the power valve is free from carbon build up. I noticed when I did the top ends on my 21 250sx n 150sx. You really had to make sure the surfaces the valves rotate on Where very clean. Or they would stick on rotation opening.
Especially the side sub exhaust port valves. At 50 hrs your due for a top end on it. Good time to take the power valve apart and clean it.
Never heard of powervalve moving from a jump ... I'd look elsewhere.
Along the lines of something coming loose though.
Yah i think it is, I cleaned it out and greased the connection. I've had it stuck on the slower map before and it isnt like that. But I don't know if there is a specific way to test that it is working?
Yeah, I took off my cylinder and and the sidecase, and I inspected the balls, gear, linkage and springs and it is all working. I can open it with a socket, it opens super smooth too. And like I said it opens on idile.
I did, I took of my cylinder and the front power valve cover/exhuast port and cleaned it up, as well as the carbon from the piston and the cylinder head. I was thinking a possible top end but I checked the compression and with conversions for altitude it was around 180-185. If anyone knows more about altitude conversions for compression let me know but from what I found it should be good. The piston had carbon on it but after I cleaned it off, it still looks very good. Same with the cylinder, super clean and still had the cross hatching.
It's pretty easy to miss-time the gear segments with the exhaust control valves. Post a picture with the left and right side-plates removed from the cylinder and I can let you know if they are assembled correctly.
It's also pretty easy to get the torque sequence wrong on the intermediate flange. That will cause the control hatch (main exhaust power valve) to bind in the cylinder.
You should be able to work the control hatch/exhaust flapper by hand, with the side-plates removed. That's how you know you got the torque sequence correct.
180-185 PSI is in the healthy range for a 250 2-stroke.
For example, a 250XC off-road bike typically has slightly lower compression than a 250SX and tests at around 180-185PSI at sea level. 180-185 sounds like you have the stock head, good ring seal, and lost about 8-10% due to altitude.
Healthy 250SX tests at around 190-200 with a stock head at sea level.
Sorry for the late response, been very busy with school
I still have not found the source of the problem, so if anyone has any ideas please let me know
It looks the the spring is in the right spot.
Pit Row
Spring end is supposed to be to the left of the left side pin.
I'm super confused. You landed hard on track which messed things up, then moved out of state, then rejetted your bike?
I can tell you 100% you will not make the same power at higher elevations vs. low elevations/sea level. A bike at higher elevations will have less air:fuel. Your jetting may be off as you likely just went off the stock settings and didn't fine tune it.
You'd be hard pressed to botch the power valve as it's a pretty robust setup. I'm guessing it's just the change in elevation that's making the bike feel less powerful.
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