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HE SHOULD KNOW: British and European champion John Mitchell introduces the 2009 Yamaha YFZ450R
Not very long ago fuel-injection was an absolute no-no on big single-cylinder engines - the evil combination of power-thudding and the dreaded "spritzer snatch" made them practically unrideable at anything less than half throttle.
So Keihin invented the superb FCR series, arguably the most efficient carburettors yet made, and everybody used those on motocross bikes and big quads.
But fuel-injection systems have come a long way since then and the biggest plus point on Yamaha's all-new-for-2009 YFZ450R racing quad - the company's first fuel-injected 450-class four-wheeler, launched in South Africa this week - is that its power delivery is actually smoother than that of the previous, FCR-fed model.
It picks up evenly from just off idle, pulls strongly with minimal vibration through a fat mid-range and gets distinctly nasty at full chat - all without any discernable steps in the power band.
What you dial in is exactly what you get, even at small throttle openings; you get just as much wheelspin and rear-end slide as you asked for and no more. Even the onset of terminal understeer on muddy surfaces is well signaled and accurately controllable on the throttle.
After just a few laps of the Dirt Bronco "flat track" outside Krugersdorp at the SA launch I was sliding the YFZ450R all over the place, learning to balance slide and traction for the smoothest possible progress around the circuit. The new Yamaquad is a superb training tool - and it's not often you can say that about a full-tilt racing machine.
Oil capacity has been reduced from 1.9 to 1.4 litres and it's now stored in a separate compartment in the crankcase, delivering all the benefits of a dry sump without the usual plumbing.
The cylinder head and barrel come straight off the 2008 YZ450F motocross bike (no more external oil lines) but with longer inlet cam duration (up from 105 to 107.5 degrees) and shorter exhaust cam timing (was 127.5 degrees, now 105) to ensure the abovementioned fat mid-range.
LIGHTER THROTTLE ACTION
There's no need for a choke; an electronically-controlled primary circuit keeps the idle revs at a busy, rather clattery 2000rpm hot or cold and the engine always fires at the first touch of the button - and that's worth the price of admission by itself, as anybody who has ever tried to kick-start an early Yamaha four-stroke motocrosser will attest.
All the thumb throttle has to do now is rotate a little butterfly rather than lift a 40mm carburettor slide, so its action is noticeably lighter and easier than on the previous model.
All that stomp gets fed through a rather heavy clutch that takes quite suddenly, close to the grip (relax, Cyril, you use it exactly once in each ride!) and a delightfully slick five-speed 'box with a short, quick throw and just enough feedback that you always know when it's in.
All three of the YFZ's I rode at the launch had equally crisp transmissions; other makers please note it can be done.
LONGER SUSPENSION TRAVEL
The previous model's tubular-steel frame has been replaced by a bolted-up chassis made of alloy castings and forgings - or almost. The section under the engine is still high-strength steel to reduce overall height and protect the underside of the crankcase.
The frame narrows in front to make space for 437mm A-arms rather than the 372mm units of the previous model, which allows longer shock travel (was 110mm, now 128mm) with reduced camber change.
The upper A-arm is tubular steel rather than cast alloy as before - it doesn't look quite as trick but it's actually lighter.
Some clever packaging has shoehorned a 15mm longer swing arm inside a 10mm shorter wheelbase for more suspension travel on the rear wheels as well (was 270mm, now 280mm).
The track has been increased by 70mm and is now close to the 1270mm maximum allowed by quad motocross regulations, while overall height has been reduced 75mm to 1095mm, making the 09 YFZ noticeably more stable than its predecessor.
THE PURSUIT OF LIGHTNESS
The latest YFZ's plastic body panels are even more minimalistic than on previous models, offering only token protection against the copious quantities of mud thrown up by the big knobblies.
They're also very thin and flimsy-looking - a signature Yamaha trait - in a Colin Chapmanesque pursuit of lightness but easily removed and replaced should they suffer terminal injury in the heat of competition.
The guitar-shaped seat, by contrast, is more deeply padded than on any other quad I've ridden with the exception of the Can-Am range - up to now only Bombardier seemed to realise that quad riders move around on less on their saddles than do enduro-bike riders.
The tapered handlebars have four-way adjustable mountings that that they reach can be set just right for the individual rider, no matter what his (or her) size or riding stance.
And this surprisingly user-friendly racing machine will indeed help any rider to raise their game, thanks to infinitely adjustable shock absorbers, superb chassis geometry and a nicely sorted, big-single engine that'll kick the competition's ass instead of yours.
Price:
R86 500.
ENGINE
Cylinders:
One.
Capacity:
449cc.
Bore x stroke:
95 x 63.4mm.
Compression ratio:
11.6:1.
Valvegear:
DOHC with five titanium overhead valves per cylinder.
Induction:
EHS electronic fuel-injection with 42mm Mikuni throttle body.
Ignition:
TCI digital electronic.
Starting:
Electric.
TRANSMISSION
Clutch:
Cable-operated multiplate wet clutch.
Transmission:
Five-speed constant-mesh gearbox with final drive by chain.
SUSPENSION
Front:
Double wishbone suspension with 44mm Kayaba piggyback shock absorbers adjustable for preload, high and low-speed compression and rebound damping.
Rear:
Remote-reservoir gas-filled Kayaba monoshock adjustable for preload, high and low-speed compression and rebound damping.
BRAKES
Front:
Discs with twin-piston floating callipers.
Rear:
Petal disc with twin-piston floating calliper.
TYRES
Front:
AT 21 x 7-10 radial.
Rear:
AT 20 x 10-9 radial.
DIMENSIONS/WEIGHT
Wheelbase:
1270mm.
Seat height:
810mm.
Wet weight:
184kg.
FUEL TANK
10 litres.
Quad from:
Yamaha SA.