Cycle News - Archive Issues - 1970's

IAbove) The stock swingarm proved to be too flexible and was replaced. We used a Pro-fab. Other good ones include OG Cross-Up or Answer Produets. IBelow) A " W or k s" pipe and Bassett Racing porting give the 250 moto close to 40 h.p. with a 4OO-rpm wider powerband, IAbove) The YZ 25014000 has the potential to win. even on the national level. with very little help.IBelow)luft reservoir keeps the shock from fading after 20 m inutes, Setting up the Yamaha YZ 2S0/400D By Dave "Wo rk ~" Miller and Jack Wright The Yamaha YZ 250 l400D has been dominating pro racing- this year, whether it was Bob Hannah diiring the Supercross series or one of the many local pros. Although Hannah proved 16 that you can win on the bike in stock fonn, there are still ch anges that can be m ade to im prove the bike on the pro level. For the junior or in termediate rider m any of these ch anges will not be necessary. Just give some thought to your ability level and wha t the changes will do . The wheels are fine for the junior or in termediate bu t start looking square after two or three m onths under a pro and will have to be replaced. We used Sun rims front and re ar with a cross four pattern on the front , while on the rear a cross -four inside pattern on a 4~ " rim was used . The wide rim gets more tire on the ground for dry hardpacked tracks and sp reads o~t the knobs for mud. Metzeler tires are the rule . For the dry, hard-packed tracks of southern California we have gone to a 3.25x2I on the front , and a 4.50 on the rear with excellent results. It ·s an expensive tir e that lasts about three races on th e rear and five on the front , and even longer on a sandy or "real dirt" track. ' One of Yamaha's strong points are the brakes. Both front and rear are excellent, but the rear might be a little too good. A few people have gone to a cable-actuated set~up to help keep th e rear brake from locking up. 1I's available from White Bros. , in Garden Grove , Cal if. A few manufacturers are testing full -floating brakes, but there are none on the market . , An area that doesn t need a lot of work a~e the f~rks. To get the d ampemng ~nd air pressur~ correct ta kes 15 m.mutes. W e d~amed the stock fork oil and poured m Bel-Ra y . LT 200 as per the Yam~ha man~al. Th~ use of s~ock me,dtum wetg~t spnngs along w1lh.14 PSt wo~~ best m the ~50. The ~O IS mor,: critical, and requtres changi ng the air pressure to suit the t~ack. Still ,. i~'s between 12 ~si and I? pSt. The poslllon of the forks t? the tnple ~Iamps ~as left. stock, but 11 can be vaned to SU1l the rider or trac~. For the ?o~·pro,. the mot~r is capable ofwmru~g with a goa<:! nder, but for the pro a little work won t hurt , especially in the competitive 250cc class. The motor was ported by Bassett Engineering to bring the power on hard.er a little . la ~~r . Alo,c,>g ~ith the portmg, Dave s Works pIpe was added and worked well with the 36mm ~ikuni. The I?orting . along wi~h th e ptpe make qune a difference m .the power. We then put it on the dyno and got these results : The stock r:n otor pulled 31 hp , the stocker with a "W orks" pipe ran out at 33 ~ hp with a 200 rpm gain in the powerband. The Basset t-port ed barrel was then slipped pn with a "Works" pipe and got 39 hp with a 400 rpm in crease in the powerbandl For th e 400 , if you feel tha t you really need it, Bassett can get similar results. Guaranteed you won 't be disappointed. To keep everything in the gearbox working right, Bel -Ray 75/80 is used. Change it every two weeks; it' s cheap ins urance for your clutch and gea rs. Also be su re to check the mag sea ls; the stockers som etimes leak. If they d o you ca n usuall y stop it by ligh tly pol ish ing the cr ank where the seal rides using a super fine crocus cloth . Sto ck , the mo tor will ru n very clean if you ta ke the time to jet an d maintain it right. A large part of this includes putting a new ring in it every two weeks . For pre-mix . we use Yamalube R in the gas at a ratio of 28:I , which is a bit richer than what they recommend but the piston and bearing life seems to be a lot longer. With this ratio the stock jetting is a little rich so we went down on th e main jet 10 points and the pilot 20 and it runs great. These are just guidelines; you might have to experiment a little. To keep the air clean, throwaway the stock fuzzy filter and install a Phase Two filter by JT Racing . They increase the air flow and don't fall apa rt after one cleaning. T he JT with the inner and outer filter element also lets you change the ou ter filter between m otos. An other thing to he lp your engine breathe be tt e r is to enlarge the air inlet in the side of the air box, it'll let it run clea ner on the low end. To keep from bending the shift shaft on your bike, ge t som e kind of fold ing shift lever . An IT 250 Yamaha lever will bolt right on a nd is the same len gth. ' A m a tt er of pe rsonal pe rference a re the clutch and brake levers. W e use Magura levers; the dogleg ~ves a smoother act ion and a little bit mo re leverage. The side panels a nd fr ont nu mber plate are made by U.F.O . They do n't do much more than make your bike look a little "Works. " The front nu mber pla te uses all the stock ca ble guides. Luft Shocks are marketing a reservoir for the monoshock that's simi la r to what Team Yamaha has been running on their factory bikes . It mounts on the swingann and comes with all the ha rdware necessary for mounting. You do have to send them your shock because they modify it slightly. Luft will send the shock back within one day so that you won't have to miss next week's race. The reservoir allows you to run th e shock softer so you can use all the travel available and mainta in constant shock action throughout an entire 40 minute moto . To begin with , make sure that the nitrogen p ressu re and da m pening are in the stock settings. Then set th e spring so that the bike sags about and that along with the Luft reservoi r should get you into the p roverbial ballpark . You want the rear wheel to return as fast as poss ible without topping the shock. The reason beh ind this is that a lot of people, right after *" they get the bik e, cl ick up the dampening two or three notches , making it a lot stiffer. But they are getting tired and when you watch them you can see why. The wheel doesn't return fast enough. { The shock, when it hits the first bump, goes down three inc hes and can only return one inch befor e it hits the next bump . Hitting the second bump compresses the suspension anoth er two inches a nd th e shock is still on ly abl e to return an inch before the next bump and the shock is just packing up and you , the ride r, are tak ing up the bumps with your back. The bike isn't really swapping bu t you get tired trying to main ta in control. So, it' s best if the wheel returns as fast as possible without top pi ng th e shock on the upstroke. The Luft reservoir will keep it from fading awa y after 20 m inutes. Who to see Ba sse tt R a ci ng , 11 58 1 A nabel . Garden Grove, Ca lif. Luft Shocks , 78 31 Alab ama II , Ca noga Pa rk , Calif. W h i.te Br os. , I I 6II -m Sa lin a z] Ga rden Grove. Calif. Co n ta ct your d ea ler for U. F. O . prod ucts. Dealers only contact John at (714) 994 ·3205. • Dave "Works " Miller, who recently turned 22, has been successful aJ a racer and tuner for the past eight years. He came into the national limelight aJ a three- time (1969-71) National Minibike Champion. H e work ed at the Flying Machine Factory in is early days, creating the "Penda, " a Honda CR125-engined Pent on .' In 19 75, Mille r went into busin ess for himself. His "Miller Mano" sold p ackage racers, pipes, po rtin g , swingarm, frame mods an d other go fast products. Dave sold the busin ess th is yea r to CH Performance Products. Now he d oes dou bl e-duty as a competitive southern California pro m ot ocrosser and a p ip e builder . Specializing in Yama ha motocrossers, Dave nonetheless does pipes for most popular MXers. If you're interested in a "Works " pipe, see your dealer, or contact Dave at (714) 992-5657 ... Ed .

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