2001 YZ250 Straight from the crate there’s nothing to match it! Riding prototype 2001 Yamaha YZ250 machinery, Jeremy McGrath and David Vuillemin together won fourteen of the sixteen races in this year’s US Supercross series, with McGrath winning the title and Vuillemin taking runner-up spot. This is exactly the kind of performance that has made the YZ250 the most respected bike on the track – indoor or outdoor – and to reaffirm its superiority the 2001 YZ250 gets the full factory treatment to its engine and chassis!

Engine

The bike’s long-stroke 66.4 x 72mm engine is fitted with a new cylinder head which gives a higher 9.1:1 compression ratio. Auxiliary scavenging port width is increased, and a redesigned piston with a lighter pin is used. Allied to the fitment of a new-shape expansion pipe as well as a redesigned crankshaft and modified connecting rod, these improvements deliver

sharper throttle response and improved power characteristics at all engine speeds. To reduce overall frictional losses the right side crankshaft oil seal design is changed, while a new shift cam and magnesium clutch cover help save weight. And for improved cooling efficiency a new water pump housing is fitted featuring a 15mm diameter channel for improved coolant flow.

Chassis

The 2001 YZ250 benefits from many improvements to its chassis design, one of the most important being a new frame. Utilising a downtube manufactured from higher-tensile steel, the latest model’s frame is both lighter and stronger.

Retaining the same proven geometry and detachable aluminium subframe, the uprated YZ250 chassis is equipped with a new 250mm floating front disc brake, lighter swinging arm and rear shock as detailed in the YZ426F Chassis section.

2001 YZ125

Ready to give 100% every time!

From Grand Prix racing through to National Championships and Youth Motocross, the Yamaha YZ125 is one of today’s main contenders. Offering a combination of high performance, precision handling and excellent reliability, the YZ125 continues to be the machine against which others are judged.

Engine

One of the most significant improvements to the YZ125’s engine is the fitment of a bigger bore Mikuni TMXc38 carburettor for the 2001 race season. A full 2mm larger than its predecessor, this new carburettor feeds fuel/air mix into the bike’s crankcase through a new high-efficiency six-lobe carbon-type reed valve. The result is stronger power across the rpm range as well as superior high-speed performance.

Complementing these changes to the intake side is a modified cylinder with reshaped exhaust and scavenging ports, as well as a redesigned YPVS valve and revised ignition characteristics.

A lot of attention has been paid to reducing frictional losses in this high-revving engine, and for enhanced performance the crankshaft diameter is reduced by 10% to 20mm, and single-lip crankshaft oil seals replace last season’s double-lip items.

Reciprocating weight is cut by the use of a new connecting rod and a lighter small-end bearing, and to improve cooling efficiency the cylinder head and cylinder have a modified coolant supply route.

Chassis

The latest YZ125 frame makes extensive use of higher-tensile steel in the construction of the downtube, head pipe and main pipe, making the 2001 design lighter and also stronger.  

  YZ250F 4-STROKE

When the first production YZ400F appeared on the racetrack in 1998 the image of the 4-stroke motocross machine changed overnight. Light, agile and delivering a wide band of hard-hitting power, the free-revving YZ400F - and its successor the YZ426F – are two of the most successful motocross machines ever produced by Yamaha, both in terms of world-wide race successes and sales volume.

Now, for the 2001 season, Yamaha announce the launch of the radical new YZ250F 4-stroke, a lightweight high-performance machine that has been designed to attract a whole new generation of riders into the rapidly growing 4-stroke scene.

YZ250F Engine

Featuring much of the advanced technology that has been developed over the past three years for the winning YZ426F, the new YZ250F 4-stroke is the most advanced quarter-litre single cylinder engine ever produced by Yamaha.

Essentially this new powerplant is a scaled-down version of the larger 426cc design, and the YZ250F’s impressive list of technical specifications underlines its close genetic link with its bigger brother.

Running with a 77mm bore and short 53.6mm stroke, the 250F’s dry sump DOHC engine is an extremely free-revving design which delivers a broad spread of useable power.

Benefiting from three inlet and two exhaust valves manufactured from lightweight titanium, the new YZ’s 12.5:1 compression 5-valve head is fed by a new FCR37 carburettor, and for optimal exhaust efficiency the YZ250F features a big-bore header pipe and aluminium silencer.

By equipping the engine with titanium valves, Yamaha’s engineers have been able to specify valve springs with a rating around 30% lower than required for steel valves, and these ‘softer’ valve springs give the new 250cc 4-stroke engine excellent response across the bike’s wide operating range.

At only 98kg dry, the ultra-light YZ250F 4-stroke weighs in at 1kg less than the 2001 YZ250 2-stroke! This remarkable feat has been achieved by the use of a slimmed-down YZ426F-type crank, a YZ125-based nine-plate clutch and a lightweight balancer mechanism, as well as a magnesium cylinder head cover and lighter engine cases.

Based on the YZ426F gearbox design, the YZ250F’s 5-speed transmission utilises an efficient 3-bar shift mechanism, allowing the rider to make optimum use of the bike’s broad powerband which peaks at around 10,500-11,000 rpm.

YZ250F Chassis

Like its new engine, the YZ250F’s new short-wheelbase chassis uses much of the proven technology seen on the 2001 YZ426F, yet at the same time this exciting new motocrosser also utilises a specially-developed lightweight frame and a range of other weight-saving components.

Featuring a newly-designed front section, the semi-double cradle frame is both lighter and shorter than the YZ426F design. The bike’s detachable aluminium subframe is identical to that fitted to the YZ426F, and like its larger-capacity stable mate the YZ250F frame is equipped with a built-in oil tank.

Running with a compact 1475mm wheelbase – 15mm less than the YZ426F – as well as 117mm of trail and a 27.1 degree caster angle, the new YZ250F chassis delivers agile and responsive handling performance, which, together with its low weight of only 98kg, ensures that this new quarter-litre 4-stroke is sure to be a serious threat to the opposition.

Rear suspension is similar to the design fitted to the YZ426F for 2001, and consists of a new lightweight swinging arm manufactured from 2.8mm aluminium operating a redesigned YZ426F-type shock absorber featuring revised valving to suit YZ250F’s lower weight. It’s the same story at the front end where the YZ426F-type upside-down forks have also been re-valved to match the YZ250F’s individual specifications.

For 2001 all of the YZ motocrossers from 125cc – 426cc including the new YZ250F will feature a larger-diameter 250mm floating front disc brake, new-design twin-pot caliper and redesigned master cylinder for enhanced performance, while the existing 240mm rear disc continues unchanged. Front tyre size is 80/100-21, while the rear is a 100/90-19, the same size as fitted to the YZ125.

Just like all the 125cc-426cc YZ models, the YZ250F 4-stroke is equipped with an 8-litre fuel tank and blue bodywork, and for 2001 all YZ machinery features a two-tone blue/black seat.

Yamaha YZ250F. Adding a new dimension to the sport.

In the same way that the YZ426F has attracted many new riders to 4-stroke racing, Yamaha believe that the new YZ250F will appeal to a wide cross-section of competition and play riders who are looking for something a little bit different.

By developing a high-performance 250cc 4-stroke, Yamaha have signalled their absolute commitment to offering the widest choice of machinery to their customers.

With its low weight, smooth power delivery and advanced engine and chassis specification, the YZ250F is one of the most exciting developments in the off road world since the launch of the original YZ400F 4-stroke. Yamaha foresee a situation arising in the near future in which various sporting federations will allow 250cc 4-strokes to compete with 125cc 2-strokes, and when this happens the YZ250F will be in a position to take on the best.

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