Yes, I love the sound of a bike screaming its little two-stroke brains out, and I’m having the most fun I’ve had on MX tracks in a long time on this KTM 125 SX. But how much can it take? I’m on my way to finding out, and here’s how it’s been going.What I had to do first was add a 6.6kg/mm rear shock spring because, well, I’m fast (or fat) for a 125 rider. It helped a lot! My second mod was to put on FMF’s Fatty pipe ($229.99) and PowerCore muffler ($119.99). Combined they gave the bike a little more boost in the mid and top. I also traded gas tanks with Art Director Joe Mckimmy’s KTM 200 XC-W. He wanted a small MX tank (since he has an extra large 3.5 tank for off-road already), and I wanted a larger tank for riding GPs and really long motos. The 2.9-gallon XC tank gets the bike past the one-hour mark and isn’t really much wider, just deeper. I can’t really tell it’s even there. So I’ve sort of made my SX into a bit of an XC.I needed the fuel range since I got a crazy hair and signed up to ride a few classes at the Racetown 395 round of the WORCS series. I had a blast in the sandy and fast conditions and even squeaked out a qualifying position for the Pro 2 Sunday afternoon race in the Open division. Not bad for a 125! But I opted to race the 40-plus class on Sunday since I should act my age (and be a sissy and ride only one hour!).
This particular bike had seen plenty of duty even before I got it, going out to other magazines and even getting abused by the shop mechanics of the KTM race team. So I suspect it has between 20-30 hours on the engine. I decided it was time for a top end. Once I got inside, the piston and rings looked used but fine with the normal wear marks. This KTM has to be one of the simplest designs to work on. The power valve is a slip-fit and requires no fuss, as long as you pay attention. (I didn’t!) The trick, I’ve learned, to keeping KTM’s two-strokes running strong is to make sure you measure and exactly replace the base gaskets to the standard (and adjustable) thickness to keep the right deck height. I did that. But I also misaligned the simple power-valve connection and was rewarded with a bike that wouldn’t rev. That’s way better than a four-stroke pushing its valves through a piston, the reward that I would have gotten if I’d made a similar mistake with a thumper engine’s cam chain. But while at the track I was able to lift the cylinder and reset the power-valve arm all in about 15 minutes. Gotta love two-strokes.I’ve got my usual array of personal preference stuff on the bike like Fasst Company Flexx bars (www.fasstco.com) and Acerbis hand guards, and I’ve been super pumped on the traction and long-lasting ability of Dunlop’s new Geomax MX-51s. Just lately I made my bike look good with a really slick (and spastic) graphics set from RidePG.com and feel happy with an Acerbis X-seat (www.acerbis.com). The bike’s dialed, and now I’m just riding it!