Cycle News - Archive Issues - 1970's

m. lc~s. nbc rJrt W=1S very heavy on getciJ)!t I,'C 4'00 CZ igh ter. Usually, the final step in the ritual was the adaptation of a .\likuni carburetor [. the back of the CZ cylinder because ih .ilrcady-at tached .j ikov loaded up at low RP:\I or when dropped. even though it also m.ide the SCo(JLer run like -a raped ape from mid-range through peak RP"l. But almost nobodv in this co un tr-v, aside from a lew pros. ever had their '4 0 0 CZ running at lop end very long or vcry often. It was SOOOD fast up there in the rev range. \L this point. the orthodox ritual usually ended. There were a few who went on with hollow axles. alloy airbo xes, and aluminum swingarms but these had to be considered the fanatics of the cult. .\ proprietary pipe. with a silencer, was a nccessi ty because the: CZ pipes didn't silence and held back some of the power-boos ting resonance waves. Whal did vou have then? You had a motocross bike built by people who had been building World Championshipwinning motocross bikes for ten years, A motocross hike that ran faster, ran longer without repair, and shifted be u er and longer than anything else outside the factory team pits, It still probably weighed about 260 pounds but the power to weig-ht ratio was not that bad. They used t o dyno the machines and lest ride them at the f'actorv in Strakoni e. The 42 HI' stamped o~ the steering head seldom was off by more than a pony or two, a difference indistinguishable 10 the rider at the peak of the power curve. Best of all, the CZ got an awful lot of it to the track, far better than most. There was enough power anyv.. here in the band to satisfv ' most motocross freaks. As other manufacturers' 500 class machmery got upda ted, usually well after the hot-selling 250s were attended to, the CZ became less of the all-conquering legend on which the cult had thrived. The CZ 400 cult eff'ectivelv went underground even while 400s cO~llinued [0 win. mainly because they never broke. Then, 111 mid·1974. American Jawa admitted that thev had some new 400s in the warehouse: They were released with much less fanfare than surrounded the new 250s with red-painted frames. yet after riding one for over a month, it seems that they offer more. For openers, they don'[ build 'em like they used to. Is that good? Bad? Read-on. Following the sequence of the orthodox ritual. the 400 CZ buyer looks first to the forks. "Iy God, they're almost I we full inches longer where it counts. There is an honest 7" of travel up front. We drained out the "Czech goop " and it turned out to be ATF (Oh, well, it was probably fish oil ATF.). The damper rods already had the damping hole drilled all the way through, so that little much-recommended mod couldn't be included ill this test. Let's see ... it already has a factory replica plastic fender on the front, and on the rear. Somebody slipped a Fittron element in 0 this airbox. We c mid replace it ith a Twin •\ir but that's pure snob erv. .\h, the infamous 10·lb. CZ ta . Hmph. That wasn 't there. either. Th coffin tank belted 10 the frame with long black leather belt is nlurni urn alloy painted a dull gray. (Why didn't they just leave it all shiny to enhance the "works" image?) The 400 was the first of the latest model CZS to have the allov tank which, than kfully, also doesn'l include lhose ugly rubber side panels. Ah. lhe rear shocks! But those are different, too. They now have a I'Motocross Specia.I" dec,d on them and different springs and bodies. Whal does il all mean? What it means is that the rear shocks \\fork acccpt.J.hly until lhcywcar out, which took us a.bout a m-ollth to accomplish. They feel harsh but progressive, all("vin~ precise control. Flash! There iti little to none of the infanlous CZ sidehop. The new swingarm. the shocks, the changed !(eometry. have all cooperated to make the nt'w 400 track slrai!:ht if somewhal riiridly. The rear end 1'0110''''$ you f'aithfullv. You always knovv where it is. · suspect I hat the flex ure inherent in seven inches of unguided travel may be To {kal with the harshness felt in the causing- some moment ary binding un the dow 0 , tro ke, \rhat you end up with in the suspension department 011 the new 400 is something dose to what the pros seem to ride with: stiff. long trave l forks and soft rear suspension, Even if, in this case, there isn't that much travel. the rear end still wouldn 't bottom. shoc ks we look off what should be, a c c o r d i ng to popular motorcycle mythology. the I 10 pound springs .md discovered that they arc in re.rli I v relatively t ame {)') pound springs. What's happening here? I'he shocks themselves arc apparcnt lv huilt to stand up to sorne serious flat -out impacting. l'hev have J. fair amount or bump damping and very stiff rebound damping, about like a 1\.0 . '1 in the fifth position..\s stiff as they .arc, they heat up preu y quickly bUI don 't seem to fade in 30 minutes of racing. though the heat probably accounts for their 4·6 week competition lifespan. The main things to be improved in the new ez's rear suspension would be to match the shocks. Just like on everv other s rock motocross hike , it's unlikely you'll get a p.iir that damp cvenlv on hoth the upstroke and downstroke. The two on our ·10 0 didn't, either. Xo t having a box of ":\!otOCTOSS Specials.' on hand, we instead relied on the intuitive suspension wizardry of a. young former CZ freak, Garv Hvrnes. lie mounted ridiculous~so~tnJi;lg 50~70 pounds progressive springs vand the shocks felt softer and worked a 101 better. There was only about two inches of actual travel left with a rider aboard OtH rhev wouldn't haltom and tracked pret.l)· darn good. Control wasn't hurl and comfort was helped. The forks seemed to gel less stiff over lime though we The orthodox ritual of the CZ CUll W~L'i obviously g'oing to have to undergo reform. Hut let's go back a minute to all the things that were ornitfed from the CZ stock to trick transition ritual. Like the engine. The CZ motor stems from a design originally conceived around 1955. It is little changed since then except to enlarge the capacity and. for that lack of change, every motocross rider should be thankful. It is one of the few engines riders will say is "fun to work on." Everything fits together snick-snick so nicely and when you take off that cylinder, some of the reasons why it wo~ks so well are revealed, There are two intake ports: the bridge between them is wide enough to make it look that way and the intake manifold is designed that way. There is also a boost port that is not too big, apparently just right because the 383cc CZ engine is still one of the fastest motors in captivity when it 's let loose. There are very big transfers, angled and chamfered and fairly smooth just as the engine comes from the factory. The Mr. MotoXR heads the CZ for the apex, able to wait very late to brake. Authenticity prevailed ijl the CN test with rider wearing Moto Klub Holice racing jersey. How much more Czech can you get? .' a: llJ t- IllJ :J r 0 z d: ..: z :J c:: u. ~ 0 .J c:: :> r I- s .J llJ OJ c, :;; d: u llJ Z d: .J i u a: ..J :> z r 0 , > m Vl 0 I- 0 r a. Siamesed exhaust port should be de-carboned fair!\, regularly if you run Castrol 20: I like the factory says you should with a CZ. The inside of a stock CZ cylinder is beautiful to behold, but not as neat as Catherine Deneuve, The head, whose external finning got radial last year, has two overlapping he m i sp h e r i c combustion chambers which previously each guided a flame front from two sparkplugs, The new 400 loses one plug and its corresponding coil but the double hemispheres remain. It's not as "right" as it should be and we wouldn't be surprised to see a new head within a few model changes. The rear PA L Czechoslovakian sparkplug is located in front of the intakes and that's the plug that starts ignition. Previously, one of the hot set-ups was to leave the very good stock PAL plug in the rear hole and put a Champion in front to complete the combustion before the gasses got out the exhaust port, as per design intent. The PAL is virtually foul-free with its recessed tip design and the sole remaining one still does a hell of a job. The halving of sparks is apparently a necessary economy measure but we wouldn't mind keeping the dual plug head that has been a CZ standard for years. They were ahead of , the mob and nobody appreciated it very much. Rejoice! (Wait til the hallelujahs die down around h ere.) The 400's incredibly reliable positive-shifting four-speed gearbox remains unchanged. The thro w" arc long and the gears are indestructible by' normal human standards. If you want to see one of the mechanical moturcvcle marvels of the 20th century, unscrew the inspection plate under the carbo and look in at the selector plate that guides the shifting to the next gear and at the gears under it. Most everybody who rode it agreed that even as a four-speed. the 400 CZ had one more gear than most people could use. All of the internal gears are bigh and closely spaced. It is all-out racer ,U1d the smallest stock counterhsaft sprocket, a 13T, will still result in using first gear on some tracks. Progression is what it always has been: excellent ratios for fast racing. On the other hand, cowtrailing it successfully requires a 34mm Mikuni and even lower gearing. While you have the inspection plate off. drain the gear oil and put in a half-liter of fresh stuff. You should do it every 3-5 races whether it needs it or not, On the other hand, we remember one Expert who ran with his CZ gearbox dry fo r a couple of weeks until he accidentally discovered there wasn't any goo in it. It's that strong a unit. None of the reliability prohIems some have noted on the 250 five-speeds are there, Some things to watch out for on the engine are cylinder mounting nuts that need re-tigh tening after every race. Otherwise, air leaks develop and a piston .0020 oversize cost $40 or so. Keep the nuts tight, gearbox oil fresh, carbon scraped off and nothing is ever likely to go wrong with this motor. Except with our test bike, something did. Cycle News had the dubious honor of having the first 400 CZ to come through American J awa that lunched a lower end» After about six hours of riding, the double left side main bearings seized into each other. As they said at Jawa, "Little problem at factory." New bearings went in (Luckily an ace Czech wrench had jus t come over from the old country because there aren't that many people around who are familiar with CZ lower ends. You just don't look at them that ~uch.) and we rode the bejeezus out of that 400 for another 50 hours without a miss. Another 400 of our acquain Lance. same engine, different frame, ran a year before it seemed ·advisable to check the rings. And that was all. The other weakness that we thought had been cured in the '74 models but hasn·t. is the magneto-flywheel ignition. CZ ignitions are like eggs. If you get a rotten one, you get rid of it and don't try to make .anything out of it. When you get a good one. you seldom stop to think about it. You just use it. Time it regularly, replace the points every ;ix Er:. "! ;I: ga .... ~ g ~ r-, O'l 25

• Cover