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/127291
GTECHNICAL Building aFormula DTX racer ~ , even p ro vid ing th e spokes. Wh ile we were there" th ey a lso mounted and bal anced o ur tires, arid installed new tubes to rep lace th e ba ttered stockers.' Wit h th e new wh eels installed, the b ik e was reall y starti ng to l o ok purposefu l. As far as the engine, our test un it 's ca rbu ret io n had a lready been u pgraded , from sta ndard RMX speci fica tio ns by o u r in- ho use endu ro gu y, Kit Palmer , , wh o 'd a lso fitted a Pro Ci rcuit expansio n chamber. It sh ould be sta ted that at th is point we didn 't have a complete set o f th e AMA 's DTX ra cing rules (see sideba r) , a nd we su bse q uently made a few m istak es. .Firstly, we wrongly assu med that th e AMA 's n i les wo ul d forbid afterma rket p ipes. And since th e stock R MX pipe , and muffler a re just too restrictive fo r race track use, we fitted the stoc k system from , again , a n RM250. Nex t, we install ed a com p ression in our gea r bags a nd headed so u th toward Ca rlsbad. ' Wh ile we' re on th e su bject of gea r, let it be kn own th at lea th ers are th e hot setup for di rt track raci ng, but mot ocross ap parel works fine for short track or IT racing. O ne piece of specialty eq u ip me nt th a t you wi ll need is a steel shoe (T rust m e here - more , .la ter), and Ken Maely is th e hot guy for hot shoes . Sign-in a t Carlsbad was low-key, to say the least. T he races, hosted by Dirt Sports P ro mo tio ns, Inc., fea tu re gokarts and mi ni sprint ca rs as well as m otorcycles, 'a nd th e bike guys all pit alo ng th e fen ce closest to th e race way . Entries were sli m, with less th an 20 bikes entered , divided int o di splacement, skill and (in some cases) age. O 'Dell, a form er speedway racer a nd AMA Expert dirt track license ho lder, wo uld ride th e bi ke in the 250cc P ro cla ss, whi le I would double u p in th e Open Ju n io r (there was no 250cc ' DTXRULES except for pa int. Han dlebars, grips A. All motorcycles mu st be approved a nd levers may be changed. by the AMA for DTX compe tition. G. Front brake may be retain ed for B. No modifi cat ions may be made to (T T) scra mb les racin g; mu st be the frame or main swingarm. remo ved or disengaged for dirt (o val) C. Frontand rear suspe nsion may be modified to lower the bike. an d ice racing. H. Any standa rd prod uction tire tha t D. T he engi ne must remain externally stock and mu st be the engine supplied is avai lable through norm al commerwith the a p proved model. Stoc k cia l cha n nels wi ll be accep ted. carb ureto r and stock airbox mu st be (Knobby tires, pro mo ters op tion) utilized (jetting perm itted), Exha ust I. Rear stock rims may be replaced. system may not emit a sou nd louder Ent ire front wheel assemb ly may be tha n 99 dBA (decibels) measured at cha ng ed. 20" a t half maximum rpm. . J. Numbers mu st he as per the current ama teur competitio n rulebook. All E. Maximum allowable overbore is other ru les will be as per the currenr .080 (of an inch) a nd the stroke may ama teur compe titio n ru le book . not be altered. The cylinder and head mu st be the same as supplied by the DTXCLASSES manufacturer. F. Fro nt fender may be removed, but I 0-85cc otherwise bodywork ,' including seat 2 86 to 125cc pan (foam may be modified) mu st 3 . . . . • • . ......... ... 126 to 250cc remai n . co m p le te a nd unmodified 4 . • • •. •.•••. •.• • • • • • 261 to 500cc straigh t, ro ll o ff th e th rottle, grab th e comp ressio n release, and back 'er in. T he co m p ression release took so me getting used to. lt emi ts a so u nd like wet Iarts , a nd it took me a few laps just to sto p la ughing. It really ge ts th e attention o f th e g uy beh ind yo u , th ou gh. Dirt track ra cing requires a much di fferent co rneri ng p ro cedu re than mo to cross i ng . o r eve n s peed way. Whi le a n MXer points a toe and a speedway racer sta nds u p with his bike more or less vertical, a dirt tracker rea lly lea ns it over , so far in fac t that he has to hold h is leg up o ut of the wa y of th e ha ndl ebars. Rid ing this way for 10 la ps 'around a sho rt track felt like doing leg lifts , so I ca n imagine what a 25-lap National must feellike l release, wh ich is useful for engine braking on short tra cks. And th ou gh a co mp ressio n release is no t spec ifica ll y against the rules, th e rules do state th at th e en gine " m us t remain externa lly stock." Ooops .. . Ne ver the less, we co n tac ted R ic k Merha r a t 202 Racing, who set us u p with a co m p ressio n release mech ani sm , cable a nd a forefinger-o per a ted Magura lever (as op posed to a thumb trigger ). 202 Racing 's spec ia lty is a type of co mpression release design ed to ease bi g-bore starti ng, but beca use his unit mounts in the cylinder wall , Merha r didn't feel it wo uld work for our application. In stead , he sent us o ne whi ch thread s into a spark p lug hol e. Now, sin ce o ur cyli nder head ha d j ust one spark pl ug hol e, we needed to have a no ther one mach ined . An d since th e engine is wat er-cooled , the machini ng wo uld ha ve to include a " th readed sleeve welded down through th e water jacket - not a n easy task. We en listed T om Burba a t Pro design to do the mac hi ne wo rk, and we were rewarded with an OEM-quality.job. The co m pression release lever was bo lted onto the left side o f .the han d lebars belo w theclutch lever, and the .ca ble carefully ro u ted so it wouldn 't snag o n a ny thi ng. Burb a also set us up wi th a tethertype kill switch wh ich , a lt ho ugh not co m mo n ly u sed by d irt tracke rs, ·is req uired o n spee dwa y bikes and is a n excellent safety measu re. Going in circles 2 The next Sat urday night, Jimmy O ' Dell a nd I load ed ou r creation into th e bac k o f my pi ckup tru ck , th rew A compression release (ri gh t) and lever (abo ve) were in stalled ' but are not necessary equipment forDTX racing. A deadmao's kill swi tch is, again , not a requirement but is a smart safety. m easure. J un ior) a nd DTX categories. DTX is not officia lly recogn ized by DSPI, so DTX win ners tra de possession o f a n ex-Ro n Wood trophy nickn a med th e " Fred Win dum Mem ori al. " (Wind um is the pe n name used by th e Cycte Neuis con tr i b u tor, w ho s ha ll remain a no ny mous. ) T he first pra ctice sessio n was paged to th e track ga te and O 'D ell too k the bi ke ou t for a sha kedown run. U po n returni ng he pronounced it race-read y and it was my turn. Of course, th e track had just been wa tered , a nd m y first sessio n was more a case of learn in g how to fall th a n ho w io slide arou nd corners. Fortunat ely, m y second session went m uc h better , a nd I actually bega n to practice wha t O 'Dell had to ld me p u t it in seco nd g ear , leave it th ere, and then, just past halfway" down th e As I a ll u d ed ea rl ie r, I ha dn 't bothered to obta in a steel shoe p rior to my first ni ght o f dirt tracking, and I soo n lea rn ed th at this was a big mi stak e. Just whe n I felt I was getti ng th e hang of th in gs, m y foot caught traction, a nd I nearly kicked myself in th e back of the head. And from th en on , if I p u t any weigh t on my leg at a ll, it wo uld try to rip my hip off! No t to ma ke excuses (well , ma ybe a little), but the fact th at I didn 't have a steel sh oe hampered m y pe rfo rmance th e rest of th e n ight. As a resu lt, I fin ished a sol id fift h in both classes - a sol id last pl ace in the five-rider fields, I m ight add. H o wever, in the Am at eur class I didn 't get bea t by m uch - it 's a mazi ng how clos e you can stay to th e guys in front. (It's even more amazing how difficult it is to pass I I I them l) The DT X class was another story. . however, as up against th e Experts, I got sa wed. T he abso lut e capperwas wh en , on the n inth la p of th e 10-lap fin al I hi t a ho le th at had developed in tu rn four a nd nea rl y clouted the crash wa ll , whi ch let the leader lap me rig h t a t th e fi n ish l ine. H ow h u m ilia ting ... Which is not to say o u r DTX Project was a fa il ur e. Au co nt ra ire. J ust to p rove th at it was me, not the bike that was Performing so mi serably, O ' Dell rode it to th e wi n in the 250cc Ex pert class, defea tin g a co uple of pure-bred dirt tra ck mach in es in th e p rocess. O 'Dell tim ed th e sta rti ng lights perfectl y and led th e field into turn one, th en " pole putted " hi s way to victory. Needl ess to say, th en, o ur project was a success . As is DTX raci ng, whose