Yamaha YZ250 YZ250H 1981 Service Manual

Dirt Bike Magazine's own history of the YZ250 places 1981 at a genuine sweet spot: "1980 and 1981... to this day, the YZ250s of this period are highly regarded and sought after. Suspension and power were excellent." Hagerty's own listing agrees these final two air-cooled years represent "among the most desirable air-cooled two-stroke Yamaha MX bikes to vintage race or collect," coming right before Dirt Bike's own account describes 1982 as a year where "everything changed, and not necessarily in a good way" — liquid cooling, an early production power-valve, and shock linkage that Dirt Bike bluntly calls mostly ineffective in that first attempt.

Cycle World's own February 1981 road test details exactly what changed for the H model, and it's genuinely refinement rather than revolution: "visually, the '81 YZ250H doesn't seem different. Refinement rather than complete change is the theme." The biggest genuine news was suspension — new KYB forks with 43mm stanchion tubes and 11.8 inches of travel, using bushings at the bottom of the stanchions and top of the sliders specifically to reduce friction and ensure smooth operation. Oil volume grew to 20.4 oz, meaning less heat buildup and more consistent damping action through a long moto, with softer and heavier fork springs available for tuning to different rider weights and track conditions.

The genuinely significant driveline change for 1981: Cycle World's own test confirms Yamaha reversed course on the previous year's six-speed gearbox, dropping back to five speeds — "the internal ratios for 1st through 5th are unchanged. Sixth is simply removed." That change freed up genuine room inside the gearbox for wider, beefed-up gears, and Cycle World's testers judged it a real improvement, since "few racers actually got to use 6th" anyway, and shifting through the remaining five ratios felt "smooth and positive." Power output was raised through porting changes and a fatter exhaust pipe, delivering more midrange torque and demanding fewer shifts per lap — genuinely useful tuning for real-world racing conditions rather than pure dyno numbers. The 249cc air-cooled two-stroke single, fed through Yamaha's reed-valve induction, ran through Yamaha's proven Monocross single-shock rear suspension — technology the YZ line had itself pioneered years earlier and that had, by 1981, become genuinely class-defining. This H-model generation represents the last air-cooled YZ250 Yamaha ever built before the liquid-cooled, power-valve-equipped era began the following year.

This factory service manual covers the procedures, torque specs, and diagrams needed to keep a 1981 YZ250H's two-stroke engine and driveline running the way Yamaha built it.