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/125804
.. • en g> l1. N .... en t> o ~ w Z w oJ U >U The JH pipe slips right on to the head pipe and tucks in neatly all around. I nstallation requires only loosening the head pipe flange to get it at the right angle. Period. One result of the Mikuni/DH reed valve set up on the 250 is smooth, strong out of the corner very easy to ride fairly competitively though the reed valve gives only a marginal horsepower advantage of the useable kind. There was also a 125 CZ available which had received a 30mm Bing carb and a Dli reed valve. Period. There was no other preparation on the bike. The reed valve seemed to make a more noticeable liP increase on the 125. Perhaps, it was the same proportion as for the 250 but any gain from a smaller displacemen t engine is 'going to be more noticeable. The Bing/reed combination again made the in-out of comers games less of a hassle but the little CZ seemed to run out of revs in each gear faster. compared to a stocker. Another approach to a hot CZ czet-up is taken by Triumph-Suzuki of Pomona, who sponsor and prepare bikes for Rex Staten. They favor an IRZ Spanish dual needle carb conversion in the 33mm dimension for the 250 and 36mm for the 400 CZ. (This is the stock carb on the Ossa.) The argument is that an IRZ is nOI as sensitive to rejetting requirements as aJikov or Mikuni. Then, a most noticeable boost in engine tractability and top end speed is gained by replacing the stock pipe with a JH Clean Sweep pipe. The pipe was designed By Jim Hoover, who was the builder of the Conley downpipes back in the days when stock CZs came with the chromed upsweeps. He started wi th has the same effect as on a 250 but it's more noticeable since so much more horsepower is made tractable. I t could really make a big CZ in to a nice trailbike, with lowered gearing, albeit a trifle costly. For a racer, il means a steady, even power flow. You can leave it in a lower gear up to the start hill so you don't loose any edge in your shift. The pipe lets you rev higher without flattening out. Power builds along with RPM way beyond what is expected. After a while, you can stop worrying over shifting, power band, etc. and concentrate on riding the course. The expansion chamber is probably the one single biggest item in affecting two-s troke engine performance, assuming the rest of the mill is at least reasonable and Jim Hoover's pipe, originally designed to make his own bikes go better, is a definite improvement. He has spent a lot of time getting it right. Whether it's the best is largely immaterial to any body who has ridden a CZ with one attached. It's good enough so that you don't think to wonder about it. It makes riding a powerful motocross machine easier, more fun, and allows you to go quicker. The powerband takes care of itself. The pipe is $54.95, admittedly an investment in increased perfonnance, and Tri-8uz of Pomona is marketing them. the old Conley design and has modified it by the trial and error, cut and weld, ride and test process to the point that a very sanitary, torque-inducing pipe is the result. What does the pipe do? It reduces any remaining low end blubbering on the 250 or 400 CZ to zero. Everything from zero RPM on up is clean and quick and smooth. Jim aJlows as how the stock pipe might be better on mid-range power, but feels that since his pipe stretches out the power band in each gear, that it's better for most riders: expert and novice. The Hoover pipe definitely provides an increase in low end that 250 CZs have been criticized for lacking. On the Hoover pipe, the stinger is a bit longer than stock and there is a large diameter, high volume main chamber (about four inches across) with sharper angled cones. The pipe incorporates an integral silencer of Hoover's own design. It is ;r perforated wall (rather than louvered) type with spun fiberglass innards and cannot b~ blown off, out, or away. He also adds a reinforcing tab along the silencer weld to inhibit vibration cracking. The Clean Sweep is quieter to the ear than a stock pipe with silencer attached, and that's good for quite a few points. The pipe tucks in very neatly without reducing ground clearance. When installed on a 400 CZ, the pipe power with no bogging or sudden pipey-ness. It's all "right there." Hand Stay • Racing • Street Soft GLOVES Othmi.ln Distributing Co. 18227 Ludlow St. Northridge, Ca. 91324 allowed more revs in each gear "'II•• S;I\~S \~••II • Ridillg Washable On the 400,CZ. the JH Clean Sweep pipe C;III" "'ill ~III Dealer Inquiries Invited (213) 363-6230 DKW - Rickman - Steen's Super "Tn Super Price '73 Bultaco Sherpa "T" 350cc Renthal Bars - 2 ply Trials Tire - Spark Arrestor '- Skid Plates - Gas Tank Sealed - Bike ;III? sent out of state 4701 EI Cajon Blvd. San Diego,Ca.92115 (714) 283·2078 \\\\1 Look at these super items! A foam fj lied vinyl cross-bar guard - a pair of dirt protective lever cover covers - and a package of nylon cable ties. Hit your cross bar just one time and this special package paid for Itself. Send check or money order for only $5.95 + 5% California Sales Tax and 25'1 postage to: HAsCOTT INDUSTRIES P.O. Box 566 EI Toro, California 92630 Distributor lnq"tiires Welcomed COTTON TRIALS: Im• • dlat. Dell.ery ~ SOUTH BAY MOTORCYCLES 1 West 35th Street National City, Ca. 92050 714/427-2434 ~ORSTEN HALLMAN••~. I RACING INC. :i: y ....... U.S. Dist. for Trelleborg Motocross tires Torsten' Hallman special design leathers & racing equipment. (714) 460·6234 1714) 460·1402 For dealer info. write or call: 5345 Timken St .. La M.... Cal. 92041. Ontario, 1972: every winner rode in Bates Leathers! Look at this lineup of champions: • Paul SmartWinner of the 250-mile Expert Race. • Kel Carruthers-Winner of the 125-mile Junior/Expert Combined Race. • Jerry Greene-Winner of the 125-mile Junior Race. • Pat Evans-Winner of the 76-mile Novice Race. We're not kidding when we say Bates Leathers suit the champions! That's because Bates Leathers fit right, feel right, never let you down. They're custom lailored just for you ... in choice top-grain leather Ihat gives you an extra margin of comfort and safety. And they're meticulously crafted for a perfect fit. Eighteen great leather colors ... 6 rough-out colors ... 6 complimentary lining colors ... and the greatest variety of stars, stripes, designs and trim you've ever seen! Come in-or write for our free full-color catalog. -nATES -~, .~.~ IjC;ltiIC Bates - the Leathers thaI SUit the Champions. Silttit • •••••••••• • • • • • • • • • • • •• •• •••• • • • • • THE BATES LEATHER SHOP BATES INDUSTRIES. INC. 701 WeSl Cowles Street Long Beach. California 90901 Name AddressCity State Zip 46