under-bracing – fashionable during the years before single-shock linkage suspension became the norm . The wheels were Dymag 18- inch mags , 3.5in ( 83mm ) wide at the front and 6.5in ( 165mm ) at the rear . The brakes were a weak point , despite being shared with the RG500 , with just single-pot calipers to do the stopping work . These were upgraded to multi-pot calipers with the second generation bike . To help cornering , ground clearance was added by mounting the engine high in the frame , tucking the Yoshimura headers into the centre beneath the engine and removing the stator from the side of the crankcases in favour of a total-loss ignition system . The case ends were then heavily chamfered . The Yoshimura engine delivered a highly respectable 130bhp at the rear sprocket at 9500rpm . It had a bore and stroke of 70 x 64.8mm ( 998cc ) and featured enlarged valves ; the inlet diameter was increased from standard by a full millimetre to 39mm , and the exhaust by a whopping 5mm to 37mm . Lightweight tappets with reverse shims under buckets ran on special camshafts with radical lobes , featuring 10.3mm inlet lift and 9.3mm on the exhaust . The camchains featured Yoshimura ’ s own special tensioner arrangement . Piston speed was critical to performance , and Yoshimura had done a lot of testing on piston and valve travel relative to crankshaft movement . The valve gear was the bike ’ s Achilles heel . The radical overlap meant that any over-rev wrought instant destruction as the valves clipped the piston and bent – something the rider would know immediately , as the engine note changed and the bike went off-song . Riders soon learned to ignore the 10,000rpm red line and change at 9500 : by then , it was falling off the torque curve and there was little to be gained by revving any harder . The stock cylinder head featured hemispherical combustion chambers and gasflowed ports , fed by four 29mm smoothbore carburettors – the latter required special sleeving to bring them down to 29mm overall ,
as the stock carb inlet was oval and ranged from 29mm to 32mm . The regulations called for standard carbs . The ignition system was by Nippondenso CDI . Compression was 11.8:1 . Generally , the engine proved to be reliable , so long as it was properly maintained with regular strip-downs and changes to key components like camchains , tensioners and pistons . Pistons were changed every 600km . The engine ’ s internals were a mix of Suzuki and Yoshimura . The crank was Suzuki-supplied and modified to prevent twist , while the conrods were also beefed up . Standard gear ratios were used except for a higher bottom gear , and the clutch was an oil-bath type , with competition plates assisted by strong springs .
RACING THE XR69 The XR69 went well , it cornered well , and , when the brakes were sorted , it also stopped well . Without throwing buckets of cash at the project , Suzuki had produced a TT F1 and endurance racer that had the measure of Honda ’ s CB900 . The XR69 stamped its mark on its debut at the seven-round international endurance series
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