Cycle News - Archive Issues - 1970's

a By Jim Gianatsis he hot Florida sunshine beat down upon our heads like a steaming ir on as we unloaded the tw o b ike s fr om the ba ck of the ye llo w an d black Yamah auler Dodge van. Yamaha ' 5 t wo factory speedsters, Bob Hannah and Rick Bur ge t t , were ab o u t to begin one of their twi ce-weekly practice sess io ns . T Both Rick and Bob's bikes wer e bo x stock 1976 Yamaha 250 YZs which after ' four weeks of thrashing still looked and performed lik e th ey were new. That was quite amazing, ,considerin g th at th ey hardly did more to the bikes than keep them washed. I co u ld see why Yamaha wouldn't let th em have any works bikes to practice on - be cause, while Rick ad m itt e d to cleaning his air filter weekly and h aving rebuilt his Monocross shock unit once, Bob did no maintenance to his at all. That morning Bob had fmally been forced to put his firs t wrench on the bike. The air filter had finally be come so overloaded with san d after abo u t 20 hours o f riding that the piston had fin ally suc cu mb ed to a slow, agonizing death. The cylin de r was unbolted, a new piston and ring were thrown in , and Hurricane Hannah was ready to ride again. When we had the engine apart, an d had taken out the air cleaners to wash them in sol vent, it was noticed that sand had been seeping between the foam filt er elements and seams in the plastic airbox housing. The base of the filter elements had never been gre ased to provide a good seal and sand had leaked around the foam. - One thing that became re adily ap paren t to any observer was the w ay their engines performed. Every time they shifted up the engine would sound like it was bogging and the bike would slow noticeably . Finally , the engine would hit its powerband, but it would still sound like it was straining as it accelerated bike and rider up to the next gear with hardly an in crease in speed. Even in second and third gears their engines didn't want to pull strongly. Ardent use of the clutch and lots of RPM seeme d the only way to make the 250 YZ move, especially in the sand. n Predecese Ricky put in his first ha lf-hour of practice and pulled in to rest. Bob had a little more time to run. As Ricky sat in the shade sipping fru it juice and taking it easy the quiet was interrupted by a horrendous thumpthy-thump-thump, and then an engine screamed at ten grand for a few se conds before it quit. Bob was just co min g to rest, sprawled out on the ground after a terrible fourth gear highside. Rick remained seated in the sh ade sipping on his fruit juice as if what had just h appened was a regular occurrence . Bob picked him sel f up off th e gro u nd and st arted loo kin g for the visor off his helmet. The scars on the front of his Bell Motostar proved the helmet's worth. Amazingly , not even the handlebars were bent , and th e en gine fired up on th e first kick as the test ride con tin ued . T he :'ne w" YZ is an updat ed MX version in disguise . Sure it had the neat ne w Kayab a du al rate air fo rks , lightweight tube swingarm and co n ical hubs. But, it also has an underpowered engine in one of the heavie st motocross bi kes on the market. The ne wYZ 250 engine is a very well designed, hi ghly so p h isticated slu g. It is bullet proof and ultra reliable, b ut at least five to 10 pounds too heavy in weight for a co mpetitive racing engine. Added to the engi ne's weight problem. is the fact that the power is poor. Up to about 4 ,000 RPM there's nothing, th en wh at power there is co mes on the p ipe so qu ic kly with so little flywheel effect that it 's difficult to co n tro l. Fortunately, Yamaha engines can easily be modified .for increased power throughout the. RPM range . When they've had such good production engines in th e past, though , it makes on e The YZ 250 has a la rge so lid look abou t it. The dual chamber air fo rk s and monoshock make it the state-ofthe-art in pr oduction ma chinery. 24

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