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/126665
~ O"l l-I V ..0 8 v >o Z Impression: 1983 Dusqvarna 51 OTX Thumpin' light, thumpin' fast By Larry Langley The last few years have been a four-stroke lover's dream. New, modem-design thumpers have been introduced by most of the major manufacturers. They've been fun, tractable, fast and stingy with gas. But heavy. The extra 30 pounds qr SO were enough to relegate the 'k four-stro kes to p Iay- b 1 e status or into their own four-stroke class. Honda's introduction of the XR350 was a serious e[£ort to drop some of the excess weight and produce a serious four-stroke race bike. Honda was somewhat successful since the XR350 16 -_ is a fine motorcycle but it demands to be ridden like a two-stroke for it to perform. Three hundred and fifty cubic centimeters is small for a bigbore four-stroke and the XR makes it power at higher rpm. It lacks the "grunt" that is generally expected of a big-bore four-stroke, but handles excellently, turns well and all in all is a fine execution in concept. But it's interesting that Honda had to limit _ .. its displacement in order to keep the weight down. Introducing the Husqvarna 5lOTX four-stroke. Fast, agile and most important, light! Husky claims 258 pounds and we believe it. We weighed it at around 270 pounds wet which is 20 or 30 pounds lighter than its competition. Right off let's admit we like the bike. A lot. But it does have a couple of flaws. However, a big, powerful 503cc motor cradled in a state-of-theart frame with excellent suspension is hard to resist. With the Japanese developing new ultra-modern, hi· tech four-strokes, who would have thought that a little Swedish factory would come up with a superior bike. ~ • • - # • - (' + While the Japanese opted for "trick" engineering (dual carbs, single shocks, etc.), the Swedes went for simplicity. They knew they wouldn't be able to outdo the big Four in space-age goodies, so they decided to go back to basics. In striving for a lean, light fourstroke motorcycle, the Husky engineers came up with a very simple, clever idea to eliminate a lot of weight in the engine, usually the biggest source of excess poundage in a fourstroke machine. How? They eliminated the oil pump and utilized the cam chain to carry oil to the overhead cam area for lubrication. Most fourstrokes rely on pressure-fed oil to lubricate the engine. Not the Husky. An ingenious reed valve system creates a vacuum in the lower end to pull the oil back down, creating a mist that also lubricates the piston, pin ~ bearings. The reed valve is located behind thecluteh and must be checked on a regular basis for wear. A worn or broken reed can cause the engine to overheat. Husqvarna recommends Bel-Ray 40-weight oil. The motor, at first glance, looks like a two-stroke, but the twin pipes. leading out of the four-valve head are a dead giveaway. especially since they lead back under each side panel and out the back into individual muffler/spark arrestor units. Dual pipes. Hmmm. How interesting. Husky must have had a good reason for doing it this way but it's beyond our comprehension. In a bike devoted to simplicity and light weight it doesn't make much sense to us to have the extra weight, and worse, the extra width the system creates. The side panel bulge that is necessary to dear the pipes requires the rider to assume a very cowboy-like bowlegged stance when riding the bike. Very annoying and very unnecessary (see sidebar). The mufflers do agood job of quieting the motor, though. Carburetion is by a 36mm DeBorto equipped with an accelerator pump. While the Honda XRs and the Yamaha TT600 opted for more complex dual-venturi units to solve the throttle response problems on their fourstrokes, Husky's simple (there's that word again) solution works and works well. We could detect no hesitation and the Dellorto carbureted cleanly throughout the rpm range. For horsepower freaks, a bigger Dellono could probably be fitted. Since a four-stroke's power delivery is deceptive (itfeels slow), we brought along a Husky 430XC for comparison. While we figured the four-stroke would run with the 430 two-stroke, we were surprised to find the fourstroke considerably faster. In fact the four-stroke ate the 430XC for lunch in a dead-stop drag race time after time. The four-stroke put the power . to:,> t~.e_ ~ound, ~ooked up a~d was