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/125876
By Larry Barnes Th e o ld m ot o cro ss bug got yo u down ? You've been racing three years and all you've go t t o sh ow for it is a broken co lla rbo ne, wasted knees and a fourth pla ce trophy from Barnhill Memorial I\IX Park. But there's sti ll something inside you that refuses to let you bl ow off racing. It's the thing th at go t you started in the first pl ace ... the thrill of c o mpe ting agai nst y o u r fellow man ast ride a fire breathing demon machine. The double incentive of st riving for superiority in both physical skill and me ch anical know how. Maybe yo u ought to t ry a different fo rm of motorcycle racing. There are a dozen other ways to get the same ego tr ip you got from motocrossing. They range from observed trials, end u ros and cross country to short track, IT and half mile. Then all the . way to the sophistication of road racing. N ow there's just got to be a niche in there for all of you if you've decided MX ain't y o ur bag. I like to road race when I can afford it and motocross wh en some pent up frustrations ne ed to b e vented . But I get the most satisfaction getting sid ew ays on a sh ort track. Mo st of all when handlebar to handlebar with a fr iend. (Sh ort trackers alw ays seem' to get to know each other.) So before motocross bums you ou t of racing en tirely , give short track some thought. Depending on a lot of things , maybe y o u can convert your MX ma chine to short tr ack. Wit h the he lp of TC Racing, we decided to co nvert a 1972 Bultaco 25 0 Pursang an d keep tr ack of wh at must be done, what coul d be done, how much it cos ts to m ak e a competitive ch ange-over. Fir st, here's a list of " m us t" parts and their approximate co st : o • Disc bra ke master cy lind er bra ck et . Tape the coil after wiring up a kill button : Her e it is, ready to ra ce . Sure is pretty. I. 19 inch fr ont wh eel assembly, $65.00 2 . handlebars $8 .00 3 . front and rear tires $30 .00 4 . leathers $200.00 5 . steel shoe $30 .00 To these you will probably add some of the following, depending o n y our seriousness and w allet : 1. square number plates $ 1.50 each o r $4.95 per set 2 . rear dis c setup $ 68 .0 0 3. foam soc k ai r clean er 55.00 -$ 7.0 0 4. 11.9 inch Koni shocks 559.95 5. full coverage helmet 5 59.95 6. spare sprockets $ 12.00 7 . trick frame 54.50 8 . oversize Mikuni ca rb $46 .00 9. short track high rpm t uned pipe, $60 .00 Now before y.ou get fre aked out o n the cost of co nvert ing, consider this list of items you will be removing from yo ur MX bike that can be sold or traded, with approximate values: 1. 21 inch front wh eel asse mb ly , 5 100 .00 2 . MX handlebars 58 .00 3. MX Iootpegs $4. 00 4 . front fender with bracket $ 15 .00 5 . stock air bo x wi th side numbe r plates $5 0. 0 0 6 . M X re a r w h eel wi th b ra ke s, . $ 100 .00 7 . rear shoc ks $ 4 0 .00 OK, no w it's tim e to ge t busy. First thing is to strip th e bi ke d own to th e frame ' and wash all th at moto cro ss grunge o ut o f th e n o o ks and crannies . Ha ck saw o ff all th e un necessary ta b s, like chain guid e mo un ts, air box mou n ts and an y th ing el se th at isn't needed . But save them in case you wan t to switch back som ed ay . You c o uld have th e frame sand blasted and painted, but it's much easier to use a spray can to sp iff it up . Sh ort trackers are supposed to b e san itary , yo u kn ow . A motocross m achine is de signed wit h lo ts of ground clearance you w on't be cu t th at angle d own co nside rab ly . T here are tw o ways: cutting th e fo rk springs o r mo vin g th e tubes up in th e trip le clamp s or bo t h. If ' yo u sh o rte ned th e ne eding or want ing on an oval track. groun d clearance o n th e track s you are Th e idea is to get as clo se to th e ground as po ssib le wi th out d raggin g. And the eas ies t w ay to accomplish thi s is to r eplace the rear shocks w ith so me shorte r models. Th e shortest shock s availab le are Koni 11. 9s . Use 60 /90 o r 70 /110 SHORT ' spring s, depen din g o n how mu ch yo u weigh . Let's le ave th e fro nt alo ne un til all th e weigh t is p ut bac k o n . No w . KO ahead and h ang th e new wh eels and handlebars. Put th e eng ine back in w ith a compressio n rel ease inst alled and an y modif icat ion s yo u might h ave co me up w it h for top end riding. A tip on fro nt ti res : use a Dunlop K·70 on " b lue groove" tr acks an d a Pirelli un iver sal on so ft cu sh io n track s. A Goodyear DT o n th e rear is standard. per fo rm ance. Tra de your air b o x in o n a Fi l Hgreen so ck fi lter. t r o n w c e n i e " Put th e scat . tan k , rear fender and ot he r stuff ba ck o n . Now get so mebody about yo ur weight to sit o n th e bike. Notice how t he front end loo ks kind of rak ed out like a chopper? .Yo u·ve got to re ar suspensio n o ne inch take tw o inch es o ut o f the fron t . Keep trimming th e fro nt en d d ow n as lo ng as you have Ever wonder w ha t th ose shoes are d oin g with a -razo r bl ad e to th eir tires? T he idea is to expose the tread · in th e directi on yo u want t ract ion . In other wo rds , expose th e tre ad o n th e le ft side of th e front tir e and th e middle tre ad o n the rear. Nex t let's wo rk on th e disc b rak e se t up . R & W Sp eci alties markets a tri ck looking kit that pra ct icall y b olts right on to Bultacos. You 'lI have to weld a brake ancho r tab, a bolt for th e right side mo unting of t he brake pedal and a master cylind er b racke t o n . Where yo u will moun t t hem will vary from bike to bike , but the mas ter cy linde r m us t be o n line wit h the brake p ed al pivot poin t. Id eally, the master cy linder ac tu a ting lever should be at the sam e angle as the brake lever p ivo t. 'O nce yo u've go t. eve rything m ounted, th e hard part co mes .. . .ge tting th e lines bl ed to m ak e eve ryt hi ng work. Hurst-Ai rhart b rak es are supposed to be easy but th e R & W unit was a real bitch to ge t all th e air o ut and functio ning. In sist o n a step b y ste p p roced u re from whomever you buy it. I won 't even tell you how three o f us took severa l hours of th ough t an d swea t to ge t the stopper working. Lessee , t ha t abou t d oes it excep t for all t he individual st uff you ' ll have to d o dep ending o n wh at bike yo u start with . I used a 60 to oth rear sprocket an d a 13 tooth co un tersh aft. I also inst alled a Sherp a T tank/ seat co mb ina ti o n and only o ne square num b er pl ate. (It was the only one in town . .Every dealer has to ns o f ova l j obs , but no sq uare o nes .] T he lim it ed rid ing ti me I've had so far o n t he Pursan g is already eno ugh to k now th at th e creatio n/conve rsio n han dl es reall y well wh en cranked over. But I'll ha ve to w ait until a few race s are unde r th e bel t to le t yo u know how co m p eti tive it/l / we are . • .. 29