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/125801
by John Huetter Photos by Larry Groves, K.C. Brintnall and Huetter The serious competitor will,. eventually, begin to modify even the best motocross machine, either adding the details the factory cannot commercially afford (for fear of pricing their product out of the general market) or to suir his personal taste and local riding conditions. There are a lot of bike shops that do a booming business adapting competition bikes to the particular needs and desires of racers. One of the more proficient outfits that has the hot set·ups for CZ and Husqvama is Valerian's Two-Cycle City in West Los Angeles. Probably the neatest item in their competition preparations is adapting a 34mm Mikunj carburetor to the big bore motocrossers from across the water. Valerian's prepares tbe Mikuni for the CZ by sligh tiy enlarging the cutaway in the sljde and rejetting it according to the riding in tended: motocross, desert, or whatever. The exact dimensions and numbers are a trade secret. Valerian '5 has spent a lot of time to get these righ t and, in actual competition, the shaped carb really performs. There is also a special manifold adaptor to fit the Mikuni. Tbe whole installation looks more sanjtary than many factory jobs. A Mikuni universal throttle cable is also req uired to fi t th e new cam. Wbile th e installation of the carb was being done, we elected to go with a nylon quick throttle, just as a nicety. The carb change, tbough perbaps the most fundamental modification, is not all that's involved with their particular hot set-up. Akront rims replace the steel stock items on the CZ (This is unnecessary on the Husky. It already bas them.) and heavier eight gauge spokes are laced into the rear rim to completely eliminate any potential spoke-shearing problems inheren t in a dirt machine in the 40 HP class. The particular bike that received the Mikuni treatmen t was to be ridden in both motocross and desert so a 3.20 X 21 Barum was opted for up front with 4.50 rubber at the rear. Suspension is something between the individual rider, his bike and the terrain. Shocks were changed on the CZ and heavier fork oil went in up front. Rubber Lodge caps replaced the plastic spark plug caps. This choice is clearly optional, based on your own experience and preference. The CZ mill was left alone. It's enough for almost .any rider, so far as power and torque range, without any modifications. In an attempt to get a more favorable borsepower-to-weigh t ratio and lower the center of gravity, steel came off and unbreakable plastic went on. Metal tan k and fenders, on almost any machine, are relatively high on the chassis compared to any other major components of mass. Reducing the weigh t up high lowers the moment of force the rider has to account for and overcome when throwing the bike through comers. Therefore, a double benefit results. The weigh t of the machjne is lowered overall and the center of gravity is lowered, which on the CZ or just about any other dirt racer, improves handling. A conservative estimate is that about 18 pounds were pared off the machine. The bike already had a silencer welded on and a Fillron installed to replace the paper barrel that comes stock in most Metamorphosis The 400 CZ captured in a moment of transition. From earth to air and from stock to modified. This test rider liked the merging of Czech, US and Japanese tech nology. European machinery. Those are both ushould do's" before ever riding your motocrosser, particularly the sound baffler. There's no perceptible power loss if you keep the stinger lengtb the same when you put the muffler on. Heavy duty cables and a brake return spring rounded out the addjtions to the CZ. These were niceties and not necessities. The cost for the cam conversion is under $60. Tbe other items' prices will vary depending on where and how much you wan t done. How does the cbanged CZ work in actual competition riding? Just bitchjn'. The Mikuni carb doesn't really add any .... . Valerian's 34mm Mikuni cam conversion, including very sana manifold, looks like a factory job. There is no skimping on quality of components. more power. [t smooths out the existent power band and allows you to run much lower in the rev range in any particular gear withou t loading up. You can also just djal it on from low RPM all the way out with no balking or stuttering from carb or engine. Nor will it load up or be hard to start if you drop it. 1;he Mjkuni's like that. The carb conversion makes the machine easier to ride and the extra two millimeters over the stock carb size seem to let the bigger engine breathe effortlessly. All that power is more tractable, more useable and more reliable. Getting the weigh t down will really help the Novice rider. You probably can't really go over in the corners any further than with a stock set-up, but the decreased weight builds rider confidence so you trY. hotter approaches and steeper angles of lean than you might otherwise. Tbat, coupled with the Mikuni which allows you to stay in a higher gear while backing off, make the CZ easier to ride fast. And it is a machine that is meant to be ridden fast. Tbe more you go, the easier it gets. The superb bandling built into the machine really becomes apparent wben you get the confidence to push it. Tbe smoothed power band, with no stuttering when you wick it on from low, or no, RPM and light weight help a lot. The other modifications are noticeable mainly for what basn't happened. No spokes have broken or even loosened significantly. The heavy du ty Makolite lined cables haven't snapped or kinked. The bigger rubber bas kept tbe front end from sinking into sand as much and, at the rear, gives a bigger footprin t to the ground. Neither tank or fenders have been ben t, damaged or dinged in some pretty serious racing. A "Flying Finn" flap keeps a lot of mud off the engine. It's all preven tive stuff and makes riding and racing that mucb less of a hassle. You will note that nothing substan tial abou t the machine was changed. The Valerian's approach is more one of refinemen t of existing good racers rather than conversion. But for the serious racer the refinements make a difference, a positive difference. And that's good news whether you're a Novice or Expert.