Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/128202
other pulling donuts in their respective Jaguar Fl and Ducati 996 hardware, before it's your turn to fire up and take to the hill. Fire up the starter with the button above the throttle and the engine immediately settles into a lusty, lumpy throb exactly like the sound of an F3 racing car. Quite quick-steering and relatively agile for a bike with such an improbable engine architecture, the CobasBMW is easy to chuck through tight corners like the Mallory chicane or the Goodwood stable complex, but it also holds a line well in a fast sweeper like Gerards or the Esses at Mallory, where you can feel the progressive-rate response of the quite softly sprung DeCarbon rear shock's linkage ironing out the bumps in the track surface. Though seemingly rather high in the frame, hence the excellent ground clearance which allows you to max out the grip from the 16-inch Avons and use a lot of angle in maintaining corner speed, the engine's location results in a bike that makes the transition from upright to full lean quickly but smoothly: It doesn't knife-edge into the comer like some big four-strokes with heavy inline motors, and the longitudinal crankshaft and shaft drive - though bereft of BMW's later Paralever solution - didn't seem to result in any strange handling quirks either. The combination of the quite rangy wheelbase and 27.S-degree head angle made for a bike that is stable in faster turns yet, thanks to the reduced trail and 16-inch front wheel, feels reasonably nimble in tighter ones. Less satisfactory is the CobasBMW's behavior under heavy braking, where the 300mm Brembo discs do a fine job of hauling the speed down, but it takes all your strength pressing hard down on the opposite 'bar to stop the BMW from sitting up under braking and understeering offline. No question that two culprits are to blame for this distinctive mid-'80s handling quirk: the 16-inch front wheel and the hydraulic anti-dive, probably set up much too hard. Moving the adjustable clip-on handlebars out and down gives a bit more physical leverage, but this is still a trait you have to watch out for - don't try trailbraking into a tum, whatever you do. else you'll miss the apex and be late on the gas for the drive out. Instead, ride it like a car and do all your stopping in a straight line before chucking the JJ-Cobas on its side into a turn with your fingers off the brake lever and the throttle already primed, then feed in the power gradually as the turn opens up. The extremely compliant power delivery from the smooth-action engine is your key to making this work - really, riding the Cobas-BMW 17 years ago was the ticket to the promised land of fuel injection that Ducati especially made us take for granted in later years. Back then, Giro's work on the engine concentrated on increasing power without sacri- ficing flexibility. Varianti Colombo in Italy came up with a set of racing camshafts for the JJ-Cobas team; this raised power from the street KI00's 90 bhp up to 108 bhp in race guise - the rest came from the modifications to the EFI, combined with an 11: 1 compression ratio to produce 122 bhp at 9400 rpm. No attempt was made to lighten the crank or otherwise modify the bottom end, but the standard pistons have been relieved on the crowns to give more clearance with the greater overlap delivered by the racing camshafts. Giro extensively ported and flowed the cylinder head, retaining the standard valves (just two per cylinder) and springs as he resisted the temptation to fit carburetors and retained the Bosch multipoint EFI and the greater management control it offers. Fine-tuning of this is accomplished by adjusting the screw on the metering unit, located atop the cylinder block, and changing the entire EFI black box for one with a greater or lesser resistance, which in tum gives a richer or weaker mixture - the detachable EPROM chips which had the same effect on Bimota and Ducati Superbikes a couple of years later hadn't yet been invented. The JJCobas team's standard unit, as fitted to the bike both times I rode it, was a "minus 10" (percent, from standard in terms of mixture strength), but they had also "minus 5: "minus 15" and "plus 5" units donated to them after Montjuich, all with a different array of diodes giving alternative carburetion characteristics. The effect of this back when I flTst came to test the bike at Calafat was literally a revelation: Until then, I'd never ridden a racing bike which had a smoother power delivery from practically zero rpm, or a crisper, more K 100 engine's flexibility and avoid the use of bottom gear except on the pits or on the line, because otherwise the bike was as well mannered as any chain-driven two-wheeler - didn't even pull the old Beemer trick of rising up and down on the suspension as I changed gear. Even so, 1 still needed to use the bottom gear for the Mallory hairpin, and while the onedown street-pattern gearchange has a good action, hitting it under braking made the back wheel chatter under reverse engine loads. Better to notch it just as you lean into the turn, then drive out just as if you were leaving a traffic light. To begin with, the JJ-Cobas team experimented with using the stock gear ratios, but by then Giro had only managed to extract 102bhp from the engine, and, moreover, usable horsepower was only available from 6000 rpm upward - it was in this form that the bikes ran at Montjuich in 1984. This exposed the gaps in the standard cluster, so Giro had a close-ratio set made with the racing bottom gear now higher than the streetbike second but retaining the original top gear ratio. It's a nice gearbox, now, even if bottom gear could still be even higher. Though the success in the Montjuic 24 Horas that it was really built for was never achieved, Carlos Cardus' victory in the Spanish Superbike series proved the Cobas-BMW had the right stuff. It's a pity that the parent German factory never went ahead with its plans to put the bike into limited production in street form or to get Bimota to develop a similar machine based on the lessons learned with the Cobas. But the untimely death at a youthful age of Stefan Pachernegg, the BMW director who actively promoted th.is option and had succeeded in getting it approved in principle by the rest of the BMW board, put an end to the idea. In retrospect, BMW really should have made more of the Cobas-BMWs than they did - but the bike exists today to show us what might have been, representing a milestone in four-stroke motorcycle evolution. For this is the first racing motorcycle fitted with electronic fuel injection and a computerized enginemanagement system, making it somewhat improbably the first racebike of the modern era that was made in Spain - with help from Germany. eN immediate throttle response and pickup. One lap at Calafat made me a believer in fuel injection, but it was only with Ducati's arrival on the scene with their "otto valvole" that this became commonplace in racing. In fact, the Cobas-BMW starts to prod'uce very usable horsepower just as the needle on the Scitsu rev counter hits the 4000-rpm mark, then keeps building progressively and quite quickly up to the 9400-rpm power peak and beyond, all without the slightest dip in that incredibly flat torque curve, nor a splutter from the Giro-designed exhaust - though there is a noticeable increase in vibration at higher rpm. However, even at a short circuit like Mallory Park, the BMW was undergeared, forcing me to back off the throttle of the longstroke motor at 10,000 rpm in top (fifth) gear down the pit straight: JJ-Cobas' team had a choice of six final-drive cardan units offering alternative overall ratios, but the one fitted to the bike in its retirement from the racetrack must have been for CaJafat - a very short circuit, indeed! The clutch is incredibly light - you can operate it with your little finger but another surprise came when I tried changing gear upward without using it. On other shaft-drive racers, like Guzzis and BMW Boxers, that's not a good idea, and even less of one is to knock the power off in the middle of a comer and feel the dreaded understeer take over. The KI00-powered racer is almost completely free of these vices, though there was some noticeable torque reaction changing down from second to bottom for the Mallory hairpin and a big thump from the transmission going in the other direction changing into second without the clutch - so you must use it. All the more reason to employ the The bike was ridden by future Grand Prix pilots Carlos Cardus and two·time 250cc World Champ Sito Pons. cue I e n e _ s • FEBRUARV 26, 2003 49