August 23, 2011
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This is the 2010 KTM 150SX the way the MXA test crew raced it. As a rule, we don’t go for exotic or expensive mods, but if push comes to shove, we will seek competent help (no matter how much it costs). Use MXA‘s mods as a guide.

Clutch. Take some time to look closely at your KTM 150SX clutch pack. There are four aluminum drive plates and two steel plates. Make sure that the two steel plates are in the center of the pack (not on the ends). As you would expect, the aluminum plates wear quicker than the steel plates and need to be checked at regular intervals (every 10 hours would be good). As the aluminum plates wear, they get thinner. It is not a bad idea to replace the four aluminum plates with four steel plates. You might lose a little feel in the clutch, but it will last three times longer (as will the tranny oil).


Fork height. If a test rider complained about understeer or oversteer, it could easily be dialed out with fork height and race sag changes. As a rule, we run the sag at 105mm in the rear and slide the forks  up and down to suit the track conditions. Jetting. The 2010 stock jetting is good for tracks up to 2500 feet. MXA runs the standard 182 main, 42 pilot and NOZI needle. We use the clip position to adjust for temperature changes (typically in the second position from the top) and run the air screw about 1-1/2 turns out. At anything below 75 degrees, we go to a 185 main or the richer NOZH needle. When in doubt?go richer.

We prefer to run the Pro Circuit silencer over the stocker.

Side panels. To enable test riders to lift the 2010 KTM 150SX onto a bike stand, we use a box-cutter to carve a curved cutout in the right side panel. This allows us to pick the bike up by the subframe.  The 2011-12 KTM 150SX’s have different plastic.

Shock. Most MXA test riders feel that the 150SX shock is very spring-rate sensitive. The best tip is to check the free sag (after setting your race sag at 105mm). If the free sag is more than 35mm, consider changing shock springs. As a rule, however, most riders will find the stock 6.3 kg/mm spring to be sufficient. We run the low-speed compression on 10 clicks out, the high-speed at 1-1/4 turns out, and the rebound on 14 clicks out.

Forks. The WP forks are undersprung for fast or heavy riders, but about right for riders under 150 pounds. Most MXA test riders prefer to replace the stock 0.42s with stiffer 0.44 kg/mm fork springs. We run the stock oil height with the compression six clicks out and the rebound 10 clicks out.

Gas cap. We take dykes and cut the locking tabs off KTM’s push-button gas cap so it works with a twist of the wrist. Maybe it’s just us, but we have trouble getting the push-button lock to work when the bike is dirty.

The stock KTM 150SX gearing is 14/50, but every MXA test rider runs 14/51.

Cylinder head. KTM offers an aftermarket cylinder head that your local dealer can order for you from KTM’s in-house Power Parts division (Part Number SXS-10-150-051). It has less compression (a 14.8cc volume compared to the stock 13.8cc volume). This is the best head for deep sand, high-speed tracks or hot weather with pump gas.


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