Cycle News - Archive Issues - 1990's

WORKBENCH By Kit Palmer Silence is golden emem ber whe n yo u bought your brand n ew d irt b i k e a nd it so u nded so qu iet a nd crispy clea n wh en yo u fir st fired it u p ? It p urred like a kitten - 'it was music to yo u r ears. Now th at you 've got a coup le "Of races , or ra cked up a few good miles wo rt h o f trail rid ing on it, yo u ha ve probably noticed tha t your no longer new dirt bike j us t doesn ' t quite so u nd as sweet as it used to. Perha ps i t so u nds a few decib els lo uder, a litt le raspy, ma ybe? O r worse yet, maybe you 've noticed that yo ur mot or cycle doesn ' t q u ite feel as powerfu l as it did. If th is so u nds fami liar to yo u , then th er e's a good cha nce th a t your m otorcycle 's sile ncer needs so m e a ttention. . F i r s t o f a ll , yo u r m o torc ycl e ' s m uffl er(s) serves more than one p urpose. O bvio us ly, the fir st is to keep you r mo torcycle quiet , h en ce the name silence r or muffler. Without silencers yo ur motorcycl e would be deaf ening. Oh , yo u m ight th ink your H o nda C R250 is lou d even with a silencer, bu t if yo u rode wi th out o ne , or with a b lo wn o u t sile ncer, yo u 'd last o n ly a few minutes before yo u ca me down with th e wor st mi gra in e headache o f yo ur life. It' s a maz ing h ow mu ch a muffler does silence a motorcycle. Secondly , motorcycl e engi nes a re designed to be used with silence rs. Un for iu na tely, many peopl e bel ieve t ha t ha vin g a lo u d m o torcycl e R increases hors epo wer - wrong! Very wrong. In fact , th e o p posite is true. Accordi ng to every muffler specialist we' ve ta lked - to , the re was a com mon den om in a tor - a bl o wn ou t o r rem oued silen ce r w ill dr ast icall y redu ce horsep ower. Wh er e off-ro ad riding is co nce rned, a qu iet motorcycle is ex tre mely irnpor, tarn due to a ll the land closure prob lem these days. A quieter dirt bik e mea ns mor e la nd to ride o n ; no isey o nes means less land. T he quieter 'we are, the less we will be noticed. Many silencers a re equi pped wi th spark a rrestors, whi ch are manda tory for o ff-road rid ing. If yo ur pl ans in cl ude trai l riding on public lands, make sure th e o u tside o f the silencer is stamped U.S . Forest ry-approv ed. If it's no t, yo u 're ridi n g ill egall y. Keeping a silence r doing its job is si m p le a nd in ex p en sive, so th ere's no exc u se not to do it. These days just abou t a ll o ff-road motorcycle mufflers are eas ily re bu ilda ble, wh ich means ih a t all th e packing inside th e sil en cer ca n be ea sily repla ced with fresh packing, A muffler has th ree main parts: the ou ter housing (us ua lly mad e ou t of a lu mi n u m, a l t ho ug h li gh twe ight car bo n fiber and plasti c bodies are emergi ng o n th e sce ne), th e core (co ns tructed o f mild steel) a n d the packing m at eri al. The packi ng mat erial is made ou t of fiberglass, simi lar to the fib ergl ass used to insulate yo ur h ouse. Insul ating fiberglass can be used to pack your sile nce r in a p inch , but is n o t reall y recommended by a f te rmar ke t co m p a n ies th at build mot orcycle mufflers, such as An swer P rodu cts a n d C ob ra . Speci all y. designed motorcycle silencer packing will last much lo nger than n ormal insula tin g fib ergl ass and cos ts aro u nd eig h t dollars a package. You 'll probably be ab le to reb u ild yo ur silence r a t lea st two times with one package. Acco rd ing to An swer Products , yo ur m oto r cycl e ' s si le ncer s ho u ld b e re packed every six to 10 hours o f use. Kee p t h is in m in d beca use yo u r mot o rcycle wo n't ge t excessivel y loud overnigh t. Instead, it ge ts louder a n d louder so gra d ua lly tha t yo u probably won't noti ce the in crease in decib els or th e decrease in power . To repack the silencer , yo u don't even have to take th e silencer o ff o f th e ex haus t p ipe. All yo u n eed to do is remove th e sc re ws (some older silen cers use ri vet s) a t th e en d o f th e outer housing an d p ull out th e inner core. Yo u d o thi s b y slow ly a n d ca refu ll y prying o ff th e end piece and keeping an eye o n a ll the parts th at co me O Ul. Some silencers use washers and/ or sp ri ngs to seat th e inner core, so reme m ber th e orde r in wh ich th ey ca me out. You al so m igh t want to wear gl o ves, because th e inner parts of th e sile nce r will be co vered with pitch bl ack oi l a nd ca rbo n . In stead of screws or ri vets , so me muffler m anufactures u se. ci rcl ips to h old the co re i n pla ce. A ci rcl ip re mova l tool is ver y ha ndy here. It ' ll mak e th e job a lo t easier. If th ere's some p acking left , carefu ll y p eel it off the core th en in spect the core for a n y damage and keep a n eye ou t for rust since th e mild steel co ns truction o f th e co re h as a tenden cy to co rr ode. It's a good idea to cor k th e end of th e sil en cer when ever you wash yo ur ' motorcycl e so wa ter doesn 't ge t ins ide it. The core can also be damaged if th e packing gets co mpletel y blo wn o u t because it will rattle a ro u nd inside the si lence r h ousing an d tweak it enou gh to ru in th e seat a fter it 's re-installed. If th e core is severel y damaged, you a re p robabl y in fo r a whole ne w silencer, which isn 't chea p. Grab a large chun k of n ew fib er gl as s pack ing a nd wra p it arou nd th e core. According to An swer Products, u se as much fiber gl ass a s yo u ca n fit in sid e th e outer h ousing. T o h old th e packing in p lace u se thread, o r light wi re , a n d wra p it a ro u n d th e fib ergl as s onto th e cor e. As yo u in sert th e core (wi th th e fib ergla ss) int o th e o u ter h ousing , twist it until it's . push ed in as far as it will go . Before a ttach in g the en d piece, pack in more .fiberglass, fill ing up any hol es. Your repacked silencer shou ld make yo ur mo torcycle n oti ceabl y quieter an d run even better. So make it a h abi t to repack yo ur muffler every six to 10 h ours - everyon e will ben efit if you do . #J III THE RESULTS AGAIII, AIIDAGAIII, AIIDAGAIII. '990CR250 55.0 =:rrPjfljl 50.0 .~ + III 1111:1 Tl'Ii I:i!:: I!::: I:;;: :": ;:;: rj ~jl!jl ili !i !!!:jljl::':' : ;;': ;I:I:l:jjij, i 45'0111~'1~i~l~j!~!l~: :1; l n 40.0 -+- 35.0 30.0 25.0 ~ 1990CR'25 ::!iHi: i:1 !iiU ijjl .: ~~!~~;j~~j~:~ ~ij~j jl;!::i i ;: -" .' . : : j;: ::;: ::; : : : ; : ~: j' ::d:!l . 1"- + i : : , " . " •• "old·,·, ·" ,· ·, 'j"+" ' :l lIn n : T l l i j ! :i T li jl.~ ': H m II :1 11.l..·..I· .. ·· .. · · , ,, .... ·j· II' 'liHi II!lillll:II::!Iii:J ili .,.. + .1" + ::l i!li]'llIPlIl:illilli jill!jjijlljl: l ll 'i lJ t r.: :: n: ,:: I: , :jl l::'I ::: :11 .• , ·n "",. ·:q l ' p: ij :II': I: :: :::: ::: 1 ' :':1': i1 .."liI . ti 1:t1 !IJi ,I'Ijt t1 :: .~ ~~,t 1:'- 1 1 I:::;i:;!:ll 1 • Jtt it t I t t t .. + 5000 6000 rooo 1000 9000 1000 0 'ng'na Rpm PSI 54.4 HP STOCK 50.7 HP FMF 49.8 HP PRO CIRCUIT 49.5 HP '990 KX250 nJ RA CING DYNQ COMPARISON SHOOlOUT 40.0 35.0 30.0 25.0 20.0 '5.0 I'S/ Il AClH C DYNQ COMflAR'SON SHOO1OUJ 60.0 55.0 50.0 + 45.0 .. ,o.o ~_ 5.00 4000 5000 6000 7000 1000 9000 10000 11000 12000 13000 40.0 35.0 30.0 25.0 20.0 4000 4500 5000 5500 6000 6500 7000 7500 1000 1500 'nglneRpm ' "g' ne Rp m PSI 35.3 HP STOCK 32.8 HP FMF 33.4 HP PRO CIRCUIT 32.9 HP PSI 56.6 HP STOCK 54.8 HP PRO CIRCUIT 52.8 HP Sometimes you have to go to the extremes to prove your product exceeds the claims of the other guys brand . And there's no better way to prove your point than to go head to head with the competition. So we took three popular box stock production bikes and three leading performance pipes to conduct a bolt-on comparison of our own. And the results above proveour point. . PSI Performance Pipes produce more horsepower over stock than any other pipe on the market. Proof in print again, and again, and again. So, what pipe are you running this year? 19

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