Jawa 90 Cross
Jawa 90 Cross
CYCLE WORLD IMPRESSION
VERSATILITY is the major asset of Jawa/ CZ. The Czechoslovakian firm produces scooters, touring bikes, and the 250-and 360-cc scramblers that are leaders in world motocross competition. From the same organization come the 500-cc Single used widely in European flat track and speedway racing, and a number of fast, unorthodox racers, including a 350-cc two-stroke Four that develops 76 bhp!
Now, added to this factory’s vast range of machinery are the Jawa 90 Cross, subject of this report, and a stablemate, the 90-cc Roadster, both with five-speed gearboxes.
The 90 powerplant is a two-stroke Single that incorporates a technical innovation never before encountered on a Czechoslovakian motorcycle-rotary valve induction. This feature distinguishes the 90 Cross and its street companion from the remainder of the Jawa/CZ line.
Unlike the majority of bikes which employ this system, the 90 Cross carries its carburetor in an exposed location above the crankcase, rather than inside a special casing joined to the crank housing. The result is an engine much slimmer than those found on many other rotary valve motorcycles. This advantage is appreciated where trails are rough and narrow.
Jawa has incorporated other non-eonventional features in the 90 Cross. Most obvious is the treatment of the front fork, which terminates at the lower end of the steering head, rather than at its upper end. Benefit of this unique design appears to be a saving in weight. At first, the bike’s front end appears spindly and fragile in comparison with other machines, but a brief ride reveals the fork feels as strong as a “full length” unit. Otherwise, the fork construction follows normal practice, with the damper contained in the lower section, and the spring housed within the rubber gaiter on the upper portion.
The fork angle is very steep, and results in very quick, light steering. In fact, steering sometimes can be a little too quick. Over bumps and jolts of a fast trail ride, the rider’s reactions can be left lagging behind.
Unusual, too, is the lack of a dual sprocket system. Two rear sprockets-one for the trail, another for the road-have become a standard feature on virtually all lightweight trail bikes. The reason is that a small displacement engine must be geared fairly tall in order to provide fast road running. This, in combination with the limited flexibility usually found on small engines, results in mediocre low speed performance in the dirt-which is where the auxiliary sprocket becomes useful. Jawa has married brisk road performance with low speed pulling power by mating the 90’s very flexible engine to a five-speed gearbox, greatly enhanced by carefully matched ratios. The 90 exhibits amazing acceleration, considering its displacement of only 88.7 ec, and a top speed of approximately 62 mph. Yet at no time during varied types of trail riding was the low gear of 25.1:1 inadequate. The Jawa even surprised test riders by storming successfully through deep sand, despite its narrow 2.75-in. section rear tire.
Another novel feature is the totally enclosed rear chain, a welcome idea that lengthens chain life, as well as the interval between the messy process of chain removal and cleaning. Rubber sleeves protect the chain lengths between gearbox and rear axle, while a metal case covers the rear sprocket. A check on chain tension can be made without removal of the sleeves. Fully enclosed chains are nothing new on motorcycles, but it is surprising that more modern machines-particularly trail bikes-are not equipped with this convenience. Imagine the abrasive mixture of mud, water, sand, and gravel that attacks an unprotected chain.
Power output of the engine is quoted as 10.5 bhp at 6500 rpm. Bore and stroke are 48 by 49 mm, and compression ratio is 8.5:1. A cast iron liner is fitted inside the aluminum barrel. A ball bearing supports each end of the crank, and the big end turns on a caged roller bearing. The gearbox is carried in unit with the engine. Primary transmission is by bevel gears, to the five-plate clutch.
Carburetion is by a 20-mm Dellorto unit, with separate float chamber. Jawa has incorporated an induction silencer under the 90’s seat, to reduce carburetion intake roar. The tubular rubber mouth of the induction silencer can be seen projecting forward from behind the right side panel.
A 12-V, 65-watt alternator serves as power source for ignition and lighting. Starting always is swift, one reason being that the kickstarter offers plenty of travel, and is geared to swing the crankshaft freely.
The engine is carried underneath a tubular steel backbone type frame. Front fork travel is approximately 4.5 in., and rear suspension units offer 3.12 in. of travel. No bash plate is fitted under the engine, but the lowest part of the crankcase is 10 in. above ground level, thus does not appear likely to suffer damage. Ground clearance of the lowest part of the bike, the center stand, is 6 in. Wheelbase is
46.5 in.
Seat height is 31.5 in., quite high for a 90-cc trail machine. Indeed, the overall riding position is odd, in that the rider sits very tall and upright. However, this is not uncomfortable, as the 90’s footpeg-to-handlebar relationship is accurate for stand-up trail riding. A complaint is that the gear lever is so short that it is impossible to reach without moving the left foot from the footpeg. Adjusting the pedal does not help, and it seems that the Jawa owner should invest a few cents in a new and much longer pedal. Gear change action itself is swift and crisp.
Steel-rimmed wheels carry 17-in. tires of 2.75-in. section, and brakes are 4.9 in. in diameter-that may not sound large, but they are fully adequate for the little Jawa. Their performance was marred by a severe judder from the front wheel which occurred only during harsh braking at low speed. Elliptical brake drums may have been the cause.
The 90 Cross also possesses minor, but useful extras, such as a lockable tool compartment under the seat, a full set of tools, a 3-pt. reserve for the generous 2.75-gal. fuel tank, simplified wiring through the use of a printed circuit board, located behind one of the side panels, as a guide for connections, and rubber-mounted engine and rear suspension, to provide damping of shocks and vibration. The bike is priced at $398, while the 90 Roadster, equipped with luggage carrier and rear footpegs, lists for $389.
