15 KTM 250SX Top End HELP!! *UPDATE*

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1/4/2018 10:38 PM

I just recently rebuilt my bike being that it’s winter time and about 10 degrees where I live. I put a Pro X piston and Gasket kit in the bike and nothing else. However once I put it together, it seems to run ALOT louder. The idle is completely normal pace but the “ping ping” is more of a “PING PING.” There is absolutely zero knocking in the motor of any kind and it has great compression and starts first kick. I’m wondering what it could possibly be, the power valve doesn’t seem like it has a right or wrong adjustment, so I’m clueless. I know 2 strokes are very temperamental with changing weather and the last time I rode it was at the end of November when it was about 50 degrees. I’m scared to just clear it out and give it hell in case it could damage the cylinder or something similar. Anyone have this same problem before or am I just a moron?!?! Thanks in advance.

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1/4/2018 11:56 PM

Sounds to me like it could just be a combination of a fresh top end and a change in temps has made it run a little crisper. How many hours had the previous piston done?

The fact it runs means that you haven't done anything drastically wrong.
Could be an idea just to go around the bike and make sure everything is tight and fitted correctly. There may be some metal to metal contact that's tinging with the vibrations from the bike making it appear to run louder.

Your manual should tell you the base setting for the powervalve adjustment. I'm sure someone else on here will know what it is.

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@russ_69

1/5/2018 6:18 AM

I replaced the stock piston and it had around 20-25 hrs. But that’s what I’m hoping. I’ll check the manual on how to adjust power valve. Draining 6 week old race gas from the tank and starting fresh May be the key as well. Open to any other suggestions

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1/5/2018 6:24 AM

Have you checked your squish? KTMs have different size base gaskets so that you can set the squish measurement correctly, and if you used an aftermarket gasket, the thickness may be different to what you had before your top end rebuild, and therefore changing your squish measurement. Easy to check and rule out, but I would do that before I did anything else. Next step after that would be to adjust the air mixture screw, and to richen the jetting as a step after that to compensate for the colder weather.

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1/5/2018 7:39 AM

Bruneval wrote:

Have you checked your squish? KTMs have different size base gaskets so that you can set the squish measurement correctly, and if you used an aftermarket gasket, the thickness may be different to what you had before your top end rebuild, and therefore changing your squish measurement. Easy to check and rule out, but I would do that before I did anything else. Next step after that would be to adjust the air mixture screw, and to richen the jetting as a step after that to compensate for the colder weather.

X2

Paw Paw

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1/5/2018 9:54 AM

Exhaust is tight in the cylinder flange (good o-rings?) and silencer is mounted tight on the exhaust pipe?

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1/5/2018 12:00 PM

seth505 wrote:

Exhaust is tight in the cylinder flange (good o-rings?) and silencer is mounted tight on the exhaust pipe?

Yepp. Exhaust has been quadruple checked and I even through my stock stuff on and it still sounded different. This weekend I’m going to try to squish measurement because my dumbass didn’t check that. First KTM I guess lol I’ll report back. Thanks guys!!

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1/5/2018 12:20 PM

Another thing KTMs are known for is frayed reeds. I would check those too as they have a tendency to chip and break on the corners.

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1/5/2018 12:57 PM

50 to 10 degrees is a big difference, like previously stated squish (one reason I prefer oem) and reeds need checking and I highly recommend checking your left crank seal, pull off stator and see if it's still sealed

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1/29/2018 7:45 PM
Edited Date/Time: 1/29/2018 7:48 PM

Update.

Thanks everyone for the advice, however the problem was absolutely miniscual lmao after double and triple checking all the above tips (which I knew were correct from the get-go) I was almost out of options. However I was going to take the whole side case cover off the clutch side to make sure the arm down in the motor that operates the power valve was functional, but when we did it I took the power valve spring cover off and it was somehow in a bind (remind you the bike ran PERFECT before rebuilding) I guess from when I disconnected the arm. As soon as I noticed this I knew that was the issue. So I reattached the spring actually lined up with the bottom “fork” and put the thing back together and it rips better than before. So after FIVE tear downs and trouble-shooting it ended up being a 30 second fix that could have been resolved by removing two bolts lmao. Just posting so no one has the same issue as myself and doesn’t do about 6-8 hrs of un needed bike work. It’s my first KTM 2 Stroke so I’m not as humiliated. The power valve would open but not close because it wasn’t attached causing the louder sound. Thanks again for all the help!

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