KTM SX125 does not want to rev out proper unloaded

kokkie7
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kokkie7
Edited Date/Time 5/19/2020 2:48pm
Hi everyone,

Since this week I do have a problem with my sx125 from 2017. The bike runs fine, starts good, good power but or doesnt want to rev out proper. Before it idd sound normaal when reving it out unloaded (sounds like: haaarrrrrrrrrrr), but for some reason it now sounds like (haarrrhaarrrrhaarrrr).

So far I checked and cleaned my carb, checked the reed valve, tried different sizes jets and needle positions, replaced air filter, new spark plug, new fresh fuel mix, new packing in muffler.

What should I check next, could it be power valve or maybe something with the ignition?

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CarlinoJoeVideo
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CarlinoJoeVideo 5/19/2020 3:24pm
5/19/2020 3:24pm
Sounds like power valve. Try taking everything apart, cleaning and lube.

F1 has some updated power valve arms that help.
XC706 5/19/2020 5:47pm
5/19/2020 5:47pm
Pull the power valve covers off and run the bike. That should give you an idea if the PV is working properly.
2
Tracktor
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Tracktor 5/20/2020 10:46am
5/20/2020 10:46am
Yup, newer KTM PV systems are finicky and need some massaging to work properly. Also, it's best to run a good quality full synthetic premix oil to avoid buildup, imo.....
kokkie7
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kokkie7 5/21/2020 5:28am
5/21/2020 5:28am
I have opened the covers of the powervalve and started the bike, but it looks like it is functioning as it should. When I rev the engine the valve goes all the way open and close. Is there anything else that can cause this problem?

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jwolfman317
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jwolfman317 5/21/2020 4:00pm
5/21/2020 4:00pm
I would take a look at your spark plug boot. It eventually wears and loses contact with the spark plug. We have an ‘18 and had this issue that caused a misfire from mid to top. The only issue with the power valve has been just after a new top end when the o-rings that are on the shaft have been replaced. This would cause it to not return to the closed position and have no bottom-end. Once the o-rings wear-in, it will work fine again.
jaguar57
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jaguar57 5/21/2020 5:44pm
5/21/2020 5:44pm
Possibly the power valve only starts sticking once the engine reaches full operating temperature. If you aren't using a fully synthetic oil then there will be carbon buildup there and you will need to take it apart and clean it all. If you want to read up on oil specs to have an informed idea of which one to use then go to www.dragonfly75.com/moto/oil.html

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