ON THE RECORD: COMPLETE TEST OF THE 1999 KTM 125SX TWO-STROKE

This story is from the January 1999 issue of Motocross Action Magazine.

1999 KTM 125SX TWO-STROKE SPECS

Engine: Water-cooled, 124.8cc, two-stroke, reed-valved engine.
Bore and stroke: 54.25mm by 54mm.
Transmission: Six-speed, wet clutch.
Suspension: 13.4-inch WP 50mm conventional forks and 11.8-inch WP shock
Wheelbase: 57.56 inches.
Claimed weight: 199.8 pounds.
Price: $4998.
Those are the tech specs, but these are the questions that most riders want the answers to:

QUESTION ONE: IS THE ’99 ENGINE FAST?

Fast enough to get from point A to point B ahead of the rest of the 125 pack. Last year’s KTM engine mimicked the power of a CR125. For ’99, Honda should have copied the KTM. With the same Honda-ish characteristics as the ’98, KTM’s ’99 125 blows the lid off of a Honda. The engine is dead down low, but it hits with authority in the middle and revs into the ionosphere.

QUESTION TWO: IS THE ’99 ENGINE BETTER THAN THE ’98?

A little. After such great success with a brand-new engine in ’98, KTM wasn’t about to dump it all and start with something different for 1999. The power characteristics are the same as in 1998–with improvements. Like Yamaha, KTM has designed a good engine. Now all they have to do is a little tinkering (like Yamaha has done since ’96) to make it great.

The 1999 KTM 125SX engine got from point A to point B faster than its competition. 

QUESTION THREE: WHAT DID KTM DO TO THE ’99 ENGINE?

Since KTM revamped the 125SX in ’98, there weren’t a lot of engines changes for 1999. However, KTM did make a few:
(1) The 125SX gets a newly designed reed block assembly. It features a two-petal reed assembly and horizontal vanes in the intake tract (a la Honda). The new reed should improve throttle response.
(2) The hydraulic clutch, which was tested on the 125SX last year, has proved to be completely reliable.
(3) To improve shifting, KTM switched to an all-new shift fork design. The 1999 shift fork uses spring loading to reduce drag and lower the friction coefficient. How? Small springs at each end of the shift shaft suspend it to allow each gear to engage without resorting to excess undercut on the dogs.

QUESTION FOUR: WHAT DO THE CHANGES MEAN?

You can shift with ease, fan the clutch to your heart’s content and feel the engine be more responsive. In 1998 the Hydraulic clutch on the 125 was the test bed for the big bikes. For ’99, it is the standard by which every clutch is measured. Easy pull, no fading and consistency make the hydraulic clutch a work of art.

KTM has come a long way in the shifting department, but they still have a little further to go. Despite the ’99 being easier to shift than the 1998, it still isn’t as responsive as a Yamaha or Suzuki. However, it is on par with the KX and light years better than the CR.

QUESTION FIVE: DOES THE ’99 REV FARTHER?

Why would you want it to? The ’98 KTM revved forever. The 1999 still revs forever.

QUESTION SIX: WHAT ABOUT THE JETTING?

Way off. For SoCal’s sea level tracks we had to lower the main jet, pilot jet and raise the clip one position to get the KTM to run crisp. This was our best setting:
Mainjet: 185
Pilot jet: 45
Needle: NOZH
Slide: 6.0
Clip: Groove number 2
Air screw: 2 turns
Note: KTM’s are very responsive to jetting changes. If your bike feels sluggish, keep changing the jetting until it barks.

The stock jetting of the KTM 125Sx carb was horrible. It took some time to clean the jetting up. 

QUESTION SEVEN: WHAT ABOUT THE NO-LINK SUSPENSION?

Don’t obsess on the lack of a rising-rate linkage. It doesn’t mean much. By positioning the shock within the known framework of a scalene triangle (one in which the sides have different lengths and angles) it is possible for KTM to duplicate the rising rate of any linkage system. The advantages of the no-link, one-sided system are: (1) Less complexity and fewer moving parts. (2) Future rising rate changes can be accomplished by moving the lower shock position (rather than redesigning a complicated linkage). (3) Shock access is excellent. (4) The one-sided shock makes room for a straighter carburetor tract.

Two years ago Ohlins developed a special twin-piston damper to use with the no-link system. So why does the KTM have a WP (White Power) shock? Three reasons: (1) KTM owns White Power. (2) Ohlins couldn’t or didn’t want to produce the shock for the price. (3) KTM licensed the technology from Ohlins and had WP build the shock.

The KTM shock features two damping pistons (instead of one). One piston is speed sensitive (to the speed of the oil rushing through it). The second piston is position sensitive (to the location of the shock shaft). How does the WP shock know which piston to listen to? A tapered rod runs down through the shock shaft and half way through the shock’s stroke the rod activates both pistons (prior to halfway only the speed-sensitive piston is operational).

QUESTION EIGHT: HOW WELL DOES THE NO-LINK WORK?

Better than most linkages. Boy, what a difference a year makes. The original No-Link PDS system was flawed from the get-go. Not due to placement, positioning or spring rates, but bad valving. One generation later KTM has sorted out the bugs, redesigned the piston and delivered a No-Link rear suspension system that is better than most of its competitors’ linkage systems.

The PDS WP no-link rear suspension always got a bad wrap, but it has its advantages.

QUESTION NINE: WHAT WAS OUR BEST SHOCK SETTING?

What was our best shock setting? For hardcore racing we recommend this shock set-up:
Spring rate: 7.6/11.0 kg/mm
Race sag: 95mm
Compression: 6 clicks out
Rebound: 14 clicks out
Notes: Common sense and years of experience tell a rider that turning the compression clicker in (clockwise) will stiffen the compression damping. Not so on a KTM. Turn the clicker out for more compression and in for less.
All in all, the ’99 PDS system receives a good rating. It works best with minimal compression damping.

QUESTION TEN: HOW GOOD ARE THE NEW FORKS?

Gone are the wimpy 45mm Marzocchi conventional forks and in their place are 50mm WP conventional forks. This is a great change. The 1998 Zokes worked well, but suffered from terminal maintenance problems. The Dutch-built WP’s work very well, without the blown seals, warped shims and questionable metallurgy of their Italian counterparts.

Is there a downside to the WP swap? Yes. Weight. The 50mm WP forks weigh 7 pounds more than the Marzocchi 45’s. Can that weight be felt? Yes, but since the WP forks work so much better, it is a small price to pay.

QUESTION 11: WHAT ARE THE BEST FORK SETTINGS?

What was our best fork setting? For hardcore racing we recommend this set-up:
Spring rate: 0.40 kg/mm
Oil height: 150mm
Compression: 11 clicks out
Rebound: 10 clicks out
Fork leg height: 3mm above triple clamp
Notes: There is something to be said about 50mm forks. Because of the 125’s smaller size, flex is slim to none. Out of the crate, KTM is the only company with good spring rates, valving and clicker settings.

1999 was a big year for the KTM 125SX. It made huge improvements to the bike and became competition for the Japanese manufactures. 

QUESTION 12: HOW DOES IT HANDLE?

Like a Japanese bike. If you were expecting the same old line about how KTM’s feel tall and flop through the turns, guess again. The KTM 125 still doesn’t crave tight turns, but it will carve when asked to. European GP testing and a slightly slack head angle keep the KTM stable on the high speed stuff.

KTM gets kudos for their aluminum bars and handlebar bend, but they fail miserably in the categories of bar height and placement. The bars feel low–so low that the sensation of going over the bars never goes away. We ditched the stock bars for a set of Honda highs. If that doesn’t work, KTM recommends switching to an Applied KTM top triple clamp that moves the bar clamps up 5mm and forward 10mm.

KTM has been fine tuning their easy access air box design for years now.

QUESTION 13: WHAT DID WE HATE?

The hate list:
(1) Color: We like orange. Orange and black is okay (although it smacks of Halloween and Harleys). However, we draw the line at orange, black and silver. Let’s lose one of the three.
(2) Fork guards: We kind of hope that WP would make a front number plate/fork guard combo similar to Suzuki’s.
(3) Front fender: Earth calling! The worst looking fender in the universe.
(4) Rear fender: The gray rear fender turns white in blotches. It gets ugly fast (plus why is it gray in the first place).
(5) Gas cap: The gas cap is too small.
(6) Radiator wings: The rear corners of the radiator wings hook on your leathers.
(7) Side panels: Whoever designed the trapezoid shape of the KTM side number plates never put a number on a bike in his life. No matter what angle you put the numbers on it’s wrong.
(8) Turning radius: When turning left, the fork tubes hit the ignition black box. Since there is no black box on the right side, the KTM can turn farther in that direction. Come on guys, move the black box.
(9) Air filter: We love the easy access airbox, but on several occasions our Twin-Air filter was pushed off the edge of the cage while pushing the D-shaped cage into the airbox. Always check around the edges for air leaks.

In 1999, KTM was one of the only manufactures using aluminum bars. However the bend was much too low. 

QUESTION 14: WHAT DID WE LIKE?

The like list:
(1) Clutch: It’s hydraulic. Good thing, because the Honda-style power requires lots of clutch work. This is the clutch of the future.
(2) Airbox: It’s cool not to have to remove the seat to get to the filter, but be very careful that the recess cage doesn’t knock it off when putting the air filter in.
(3) Handlebars: The bars are aluminum–very cool, but too low.
(4) Tires: Bridgestone M77/78 are very good intermediate terrain tires. We like this sneaker combo.
(5) Silencer: Very quiet. When you combine the lack of low-end and the absence of sound, it’s eerie. You gas it just to make sure it’s running.
(6) Frame guards: KTM and Kawasaki are the only manufacturers to include plastic frame guards to protect the paint on the tubes.
(7) Brakes: We have often referred to KTM brakes as “Euro brakes.” What are Euro brakes? Ones that you have to pull on with more effort than “Japanese brakes.” For ’99 the KTM brakes are powerful enough to avoid the Euro nomenclature. The front is powerful and, for a change, the rear isn’t a light switch.
(8) Shock preload: Instead of two interlocking preload rings, KTM uses one thick single ring (which clamps to the shock body via an Allen bolt). To adjust the spring preload you loosen the Allen bolt, turn the preload to the correct sag and then tighten the Allen. However, you can’t tighten the Allen if you don’t make a full revolution with the preload ring.

QUESTION 15: WHAT DO WE REALLY THINK?

Let’s review.
Engine: Like a Honda but better. Don’t try and lug the KTM. Once you get in the midrange you will be infatuated, and when you hit the top end you will think it’s true love. This is a good midrange and up engine.
Handling: Sitting on the KTM it feels tall. Riding it you think the front is too low. Once you fix the handlebar problem with a new set of bars, you will find a bike that does nothing remarkably good or bad.
Suspension: This bike has top-notch suspension. The new 50mm WP Extreme forks handle small and big bumps alike. The rear suspension, although not as silky smooth as the front, handles bumps with a consistent demeanor as long as you don’t get confused and turn the compression adjuster the wrong way.
Overall rating: Last year KTM shocked everyone with a 125 that was competitive with the Big Four. This year, the KTM isn’t just competitive, it’s better than most of the big four. Welcome to the party.