engine was a four-stroke, four-valve OHC, "Pentroof" engine. The bike had a conventional 18" rear wheel but an unusual 23" front wheel which was supposed to be better for riding over potholes and ruts. The 23" size proved unpopular and did not catch on as the wheel/tyre assembly was heavy, and there was little choice of replacement 23" tyres. In 1981 Honda introduced 'Pro-Link’ models, with rising-rate single-shock rear suspension, a 17" rear wheel and a 21" front wheel. Unusual for a four-stroke with its typical intake and exhaust valves, the 1981 and 1982 XR-500 utilized a six-petal reed valve set-up between the carburetor and the intake valves. This was intended to provide better low-end performance while still allowing a large carburetor to be used. The 1982 XR 500RC was very similar to the 1981 RB apart from decal and trim changes. The 1983 XR500R was thoroughly revised with a new dry-sump RFVC 5-speed engine which was lighter and more powerful than the older engine. Induction was by 2 carburetors, the first in use until 1/4 throttle, whereupon the second started to take effect. Power was 41hp @6000 rpm, torque was 4.7 kg-m (34 lb-ft) at 5500 rpm, and dry weight was 266.7lbs. The frame was entirely revised, and suspension was updated with 43mm air-adjustable forks with 11" of suspension travel both front and rear. Wheels were 21" front and 17" rear. The fuel tank had a 12 litre capacity, the front brake was a single hydraulic disc, and the handlebars sported plastic ‘bark-buster’ hand protectors. The 1984 XR500RE model was the last 500cc XR, being superseded in 1985 by the larger Honda XR 600RF. XR 600R The XR 600R was used in Baja races. It was introduced in 1985, and was updated in 1988 when the original dual progressively opening carburetors were replaced with a larger single carburetor and the rear brake was updated to a disc. The 600 was updated again in 1992. The XR won many desert races in the hands of Johnny Campbell and GNCC races in the hands of Scott Summers. Its engine was very similar to the XR 400 and XR 250 engines, (though larger and heavier). 600's responded well to modification. A common modification was to bore the cylinder to 100mm thereby increasing displacement to 628cc. HRC produced a "Power Up" kit that included a billet 100mm piston, a revised primary gear ratio