Cycle News - Archive Issues - 1980's

Mike Beier~8 National YZ125L Yamaha: Adding the zing By Kit Palmer There is hope for the Yamaha YZ125L. Several one hundred dollar bills and a couple of hours in the garage can turn the YZ into a national caliber weapon. The proof is Yamaha support rider Mike Beier, currently third in the 125cc National points behind Kawasaki's Jeff Ward and Hon- 18 nipples, running from th rim through the hub eyelet and back up to the other side of the rim. The Zspokes cure the old Yamaha problem of collapsed wheels on tracks wi th big jumps. At least we didn't have any trouble with breaking or even loosening spokes. However, a few pros on the National circuit have broken Z- poke wheels. Earlier we mentioned the shift lever return spring pin, pointing out that its breakage wouldn't cause a maLO DNF. But our test bike's right-side chain adj uster broke, and that would cause a DNF. It seems that the puller - the part the adj uster bolt screws into - broke, allowing the axle LO slide forward; that in turn made the chain very loose. Fortunately the chain did not derail. Chain adjuster failures have been a problem with larger YZs, although company spokesmen say it's rare on 125s. Pulling three phillips head screws and one nut makes it possible to remove the air cleaner. The air box is well sealed and keeps dirt and water out, although many riders enlarge the intake for more air now. The filter itself is oiled foam with a coarse texture, and it looks like it will last for a long time. Yamaha recommends replacing the piston rings after every third race, and the piston itseH every fifth race. Details are first rate. The grips are comfonableanddon't fall apart after a few rides. Bmh the clutch and front brake levers have dogleg bends. ew red and black tank decals don't bubble up, although they do get tom by the rider's knees after a (ew rides. The bright, yellow plastic fenders and radiator shrouds have a smooth, glossy finish and hold up well in crashes. But the separate, unallached sidestand is clumsy to use. On the other hand, the 80-pageowner's manual is full of helpful diagrams, photo andtables-it'sex ellenl.There' also a race-prep and lUning guide dealing with suspension tuning, jetting and other competition tips. All that won't make the YZf25L a winner in its class. Every advantage or disadvantage is a big deal in the I 25cc class, probably the most competitive competition in motocross. The YZ has a few advantages, but the lack of power outweighs every advantage and then some. There's not enough power to take advantage of the handling, and the handling isn't so good that it can make up for the lack of power. Making the YZI25L really workthat is, making it produce enough power to be competitive - will take time and money, more time and money than most people have. • da's Johnny O'Mara. We recently had the chan e to take a few hot laps on Beier's Yamaha and found out what makes his YZ one of the most competitive machines on the circuil. The first mod Beier made to his YZ was enlarging the air intake of the "airbox by cutting the outer rim and a small section. on the left side panel. This let the bike breathe beller. and the clip on the jet needle was dropped one notch. An aftermarket pipe is a must for the YZ. Beier's bike is equipped with PSI expansion chamber. which he feels is the best for the YZ . Instead of buyinga new pipe. many riders cut the stock pipe in half at the wide t point of the header, removin tOmm to 20mm before the pipe is welded back together. According to Beier this trick works but not as well as a new pipe. The stock cylinder was trashed for an "L" chrome-bore, hop-up-kit barrel poned by Paul Thede of Paul Thede Race Te h. The barrel comes in kit form only, including pipe, piston and ri ng set, head and base gaskets, intake manifold anda main and needle jel. (Look for details on the hop up kit in a future issue). Beier' uses a 38mm Mikuni carburetor over the stock 36mm. But Thede said a larger carb is not necessary, because the stock carb can be rejelled to suit the needs of the pipe and porting. The reed valve cage was modified, and Boyesen fiber reeds replaced the stockers. The fiber reeds are more sensitive to throllie response, aidjng low end; fiber reeds also won't ruin an engine if they break (steel reeds will). Thede also did all the suspension work. The rear shock was revalved to relieve low speed damping over the smaller bumps; it was speeded up for the bigger bumps. Beier weighs around 150 pounds, so an optional heavier spring from Yamaha is fitted. The stock oil is changed for hightech Spectro suspension [Juid which can't be found on the shelves of your local motorcycle shop. The trick oil is very resistant to heat fade. The fork was revalved for the same reasons as the shock, and 10 Wl. Spectra fork oil is used measured atl40mm below the compressed fork tubes without springs. No air pressure is used. Beier's Yamaha is a rocketship. Although some low end was sacrificed, mid-range and top end power more than made up for il. The power comes'on strong but is smooth enough not wear out the rider. The only problem is that Beier's cI utch slips badly when cold. When it warms up, the slipping gradually became beller but nevercomplctely went away. The slippage mainly a cured in (irst and second gears, but the YZ hooked up from third gear and on. Even though the stock YZ suspension is very good. Beier's Yamaha is much better. Sitting on the bike, the rear end seems too springy and sofl. On the track, though, that mushy feeling goes away. Over sharp little bumps. the YZ is very smooth, and the same goes for the larger whoops. Every now and then. the rear end would bOllom, but not harshly. Here is the price breakdown 1.0 havea stock YZ buill. like Beier's from Paul Thede Race Tech: Porting $390 Shock Revalving (no spring) $132 Spring modification $35 Shock oil $12 Fork revalving $35 Fork revalving assembly $30 Other pans used: Hop up kit (only cylinder used on Beier's YZ) $390 For more info. contact Paul Thede of Paul Thede Race Tech: 714/ 594-7755.

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