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/125856
ASKE.C. ~ ( Got a technica l problem that needs expert advice? Send .q ueries to "ASK E.C." c/o Cycl e News, Box 498, Lon g Beach, Ca. 9 0801. You r reply will appear in th e pap er within a few weeks. - ' i: 0- -< Write for our brochure on these and other products, and names of your local distributor or dealer. By E. C. Birt Yamaha among the reeds 6_ I I' ve go t a Yama ha / 25 wi th a reed valve. Th e engine is as trick as can be but it sums th e real trick is ge tting it to id le. When I start it, it revs to abo u t / 0,000 RPM. Th e slid e isn 't in backward s, th e cable isn 't kink ed, and th e slide is all the way d own and staying th ere. Th is happens wi th the choke on. With th e choke off, th e bik e doesn't run. I'm using a 28 mm Nogu chi Miku ni carbo I'm stu mped, so I d ecided to ask an ex pert and yo ur name came to mind because th e guys at "Dirt Bik e" magaz ine say yo u 're a genius and I believe them. REIN FORCED POLYSTE R MOTOR CYCLE COMPONENTS. 1572 SOQUEL DR.. SANTA CRUZ. CALI FORNIA 95060 (4081476-4566 JiL David Enama Willow Grov e, Pa. DIG PERFORMANCE Dave . so u n ds to m e your vergasser is vergassing through t he wrong holes. I th in k your p rob lem is n o t an air leak , but t he pil ot jet is ei ther pl ugged o r is too small. As you sa y , the trick is to get it to id le. So let's go after the problem in steps. If y ou had an ai r leak it wo ul d m ost likel y id le fast all t he tim e. Since it dies as soon as yo u close t he ch o ke, that makes me thin k that it's the p ilo t j et. The choke passage co mes straigh t off the bowl of th e ca rb and is open as lon g as th e c hoke is o n. Th e idl e circ ui t is m et ered thr ough th e pil o t je t and handles id le and lo w e nd j etting. Where's the pil ot jet? Remove th e carbo Now remove th e float bowl, j us t back o f th e main j et bl o ck yo u can sec the he ad o f a sm al l je t se lling d own ins id e -.a sma ll pa ssage j us t ba ck o f th e needl e jet housin g and main je t holder. Remo ve th e j et fro m t he passa gew ay (t um t o th e left to un scr ew ). After yo u ge t it o u t yo u will see a small num be r sta m pe d on th e side of th e jet. Writ e t his num ber dow n fo r lat er tuning nee d s. Now witb th e jet ou t look a t all th e lillie hol es a nd see if th ey a re p lugged . Don 'f jab arou nd at these h o le s wit h an ice pick to un clog, T he size of t hese holes is what co n t ro ls th e jet size. Clean ve ry gently with a needl e an d toothb ru sh, Check the passage way itself - by b lowing air thro ugh it t o be su re it is open. Afte r you know the ear b is clean an d .no t h in g is p lugged is a good ti me to set th e floats. Reassembl e t he ca rb and pu t it bac k o n th e bike. You say t ha t it sti ll won 't id le ? Remem b er that num be r t ha t w e w ro te d own ? Le t 's ass ume th e number was 25 , pilot j ets usu all y come in steps o f 5 , like 25 ,3 0 ,35, a nd o n up. If it won't run o n th e number 25 pil ot, it m ight on th e num ber 3 0 but would m or e t ba n likel y he too lean o n th e b ot tom end to produce go o d pow er. So go up Iwo ste ps al a lim e till it id les. Now you sa y it idles, bUI b ow d o you know if it' s ric h o r lean on th e v b ot torn ? As a rule o f thumb, whe n you dr ive in to a turn and th e e ng ine bogs wh e n yo u ,.::ra h a h and ful it 's a good sign that yo u 're st ill lean . If it lo ad s up a nd die s o r is tumhl y o ff th e bot torn. th en it 's to o rich. so come d o wn o ne ste p. II' all else fai ls, you ca n reso rt to the T o m C u l p Too l , Pa r t num be r 711 4 3 3WIIA~IY ( rive lb . ha m mer) . No l really, try a not her carb . You c-ou ld ha ve a [actorv d e fec t th at no one can sec. It dues ha p pen. • SPECIALTl ES,,,,- FO R SUPER 1011 COOLING r OA HONDA ELSI NOR E CR 12!) SOO N AV AIL AB LE FOR CR2 50 McDo uga l br ing s in Hond a 125 for FIRST in CMC ! Bruce McD ougal. ren owned 125 « oc r. caotuees a II r sHl me · ever W in l or a Hon da 125 In CMC co mp etit io n Mc Do uga l. RADIAL HEAD! A NNOUNCING THE now nd lng lo r Am enc nn Honda . IS o nl y o ne 0 1 Iht· m.l n y crca t na mes ha Ving ri d d en on ra c Ing tra ms und(' , ttl!' e~ p'6'f l qu ro an ce c tr onm ma nager. Dan Hangs!c·ben. Th e R.l d hl 1 Head IS il r e volu t iona ry mn ova non lor Ih e Hon da . Deve lo ped by Don Hanqsteben . thi s new np p roa c f to hea d oesrcn p re ve n ts nea t b uild- up b y p e r rrutun q n e a t t o c. s s .co t e mo re eff iCIently . Th e rndm ! appro.ref 10 mcr ensmq oert o rrnan ce by c on lr oll m g heat w as deve lo pe d fo r the Hond a by Da n while he 1I\',1 S mnn n qmq winning team s c onsrstmq 0 1 suc h ud e ts as : Bru ce M cD ou g;'ll . M.lrk Tvre. 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