2009 KTM 125SX

2009 KTM 125 SX: Refinement of KTM's Lightweight Two-Stroke

The 2009 KTM 125 SX was primarily a refinement of the existing generation rather than a major redesign. KTM retained the compact 124.8 cc two-stroke engine, lightweight chrome-molybdenum chassis and WP suspension package introduced and developed over the previous seasons, concentrating instead on improving setup, durability and overall race performance.

The engine continued with its 54.0 x 54.5 mm bore and stroke, six-speed gearbox and hydraulically operated clutch. A 39 mm Keihin PWK carburettor supplied the mixture through reed-valve induction, while KTM's exhaust power-valve system helped broaden an engine that still rewarded aggressive riding and high rpm. Owners maintaining ageing original carburettors can compare alternatives using the MXOwners carburettor reference.

Suspension remained WP at both ends, with a 48 mm closed-cartridge fork providing 300 mm of travel and a linkless PDS rear shock offering around 335 mm. Correct spring preload, sag and fork setup remained important to getting the best from the sharp-handling KTM. The MXOwners fork oil reference is useful when servicing or returning modified forks to a known baseline.

At around 91 kg without fuel, the 2009 125 SX remained extremely light and responsive. It arrived during a period when many manufacturers were concentrating heavily on four-strokes, yet KTM continued refining its two-stroke motocross range. That persistence helped ensure the 125 SX remained a serious race bike rather than becoming an outdated entry-level model.