top of page
  • Writer's pictureCharles Lytle

The 2017 KTM 250SX is the King of Two Strokes

Dave Hose Photo^ at 408MX San Jose, CA

Well it has been some time and an unusually long winter here in Boise. I was fortunate enough to get down to SoCal and ride LACR, and 408MX in San Jose, Ca while the snow fell here in Idaho.

The KTM now sits with about 20 hours on the clock. A LOT has changed with the bike. The addition of a new Pro Circuit silencer, perfect jetting specs for 2500 & sea-level, a reed failure and more have all taken place and will be the highlights of this blog post.

Perhaps most importantly, I am fully comfortable in this bike now. The suspension is dialed and boy was I wrong about what I thought I felt in blog post #2, or #3....The AER 48 fork is just, well, awesome.

This bike to me, is so damn good that I finally built up the courage to sell my YZ250. Something I swore I'd never do!

Let's get started!


The Mikuni has been a bit of a hot mess this year. I personally believe more so on the smaller displacement bikes such as the 125SX and 150SX. Just too damn rich. I did find my happy place though and aside from swapping from 2500' settings to sea-level settings, all was well.

SEA-LEVEL: The stock specs are listed in previous blog entries and with the addition of a 450 main jet, you're good to go! Swap that main and "Let er eat", ahem... Cooper Webb said it so it must be cool. Anyway...yeah...

2500' SPECS:

***I'm going to check my notes and come back to this portion. It's a needle swap and a pilot jet to make the 250SX feel at home in Boise, ID.

Pro Circuit R-304 Silencer: BUY ONE NOW, actually BUY ONE FROM ME, mXrevival ;) We have them in stock as well as just about anything else you might want for a bike.

This pipe not only made the 250SX sound better, but added that over-rev I craved. It was just enough to send it a little further on some jumps that I just wasn't clearnig when 3rd gear wide open. The YZ250 was the baseline for measurement in this regard and was piped/ jetted properly & had no issues with these same jumps.

Once the silencer was added, I was very pleased! I'm still running the stock head pipe/ expansion chamber.


At approx 11 hours on the clock, the 250SX suffered a reed failure. I didn't know what to make of it at first as I'd never actually had a reed fail. I assumed I had a fouled plug as the carb was not jetted for a new riding area of about 5,500' in elevation. No worries, right? I'll just coast back to the truck and throw a plug in. Well, that didn't do the trick and after lots of kicking, plus checks and head scratching, I finally called it and headed back to the shop.

After removing the reed cage I was shocked to find one entire reed petal was just gone, see ya, where the F%$k is this thing? Oh sweet, my crank was hungry..."let er eat" huh? Thanks Coop.

After closer inspection, a second petal was cracking across the base where it mounts to the reed cage. It was on its way to oblivion as well. The petal that was missing broke clean across the base.

I inspected the cylinder and head and thankfully no damage. The petal was processed and ejected via my new R-304. One with the earth.

I ordered an new set of reeds for a 2016 250SX because, at the time there weren't really any parts ready for purchase for the 2017. I got lucky, the reed petals for a 2016 will fit your 2017. They're identical. I was not as lucky with the reed cage gasket, as the shape has changed. A little Yamabond sealant to the rescue and I was in business.

I hope the 4 new reed petals are doing alright in there with the 10 hours they now have since I replaced them. I'll find out very soon though as I'll throw a new piston in around the 30 hour mark.

Tidbit: In 2014 KTM decided to give VForce reed cages the boot. They had come standard on KTM for several years before that. The modern day reeds are supplied by Boyesen, and held within a cage KTM now makes that is a clone of the VForce cage.

Enough about that! I hope it was a freak thing and you guys aren't having similar issues.


Ahh, AER 48. I love em. Really, they are very good, great even.

See, in earlier blog posts I prescribed what I though was the cure to my small ailment with them. I FELT like they were blowing through the stroke, thus prompting all 225lbs of me to ADD PSI into the fork. No, no, wrong move.

The sensation I felt wasn't that I was blowing through the stroke. What was really happening was that the fork wasn't going through the stroke at all! The sensation of your forks bottoming out quickly is very similar to the feel of your forks just stopping dead in the middle of their travel. TOO MUCH PSI! I had been adding air to alieviate the symptoms and making it worse.

Thtee things clued me in on this:

1. The rear of the bike was G-ing out again and had been stable with the addition of the rear spring for my weight & a high speed compression adjustment (17mm nut on your shock).

2. I saw a photo of myself riding up a jump face with the forks stuck in the middle of their stroke and the rear of the bike nearly bottomed out.

So, the bike became unstable and therefore out of balance. The excess PSI in the fork was also adding a rearward bias to the 250SX and forcing the shock to G-out.

3. Dust lines on the lower stanchions. I started to notice that the forks weren't cleaning the fork tubes off all the way via the dust that remained clinging to the lower fork tubes after a jump landing for example. The forks were absolutely not using their entire stroke.

The fix: Simply lower the forks PSI down in two PSI increments until they truly bottom out or use their entire length of travel. I'm now running 145 PSI and the compression clickers are dialed waaay out, on the soft side. The fork is excellent. It is plush in chop and doesn't bottom on bigger hits/ jumps. I am so happy with these forks and therefore the bike. It has just gotten better with time.


Thanks for reading! I hope these entries help you guys out. If you have any questions, simply find the "contact us" link on the site above. I'm available for you guys anytime and always do my best to help.

I'm excited to announce the install of our newest product line into our 2017 250SX. The Lectron Carburetor! No jets! Now in stock for just about any relevant two-stroke! Screw you, Mikuni!

Full Lectron ride test & review coming very soon!

-Charles/ MXR

241 views0 comments


bottom of page