Cycle News - Archive Issues - 1980's

In stock form. the 1987 Suzuki RM125 has sufficient power but would definitely benefit from more m idrange and top end power. Pro Circuit ports and lowers the cylinder. mills the head and installs a new exhaust pipe. The result is a RM that hauls. The reed block spacer helps maintain low end. The Keihin carburates better than the stock Mikuni and is easier t o jet. Hop-up: The Pro Circuit Suzuki RM 125 - - -- Breathing a little ffre into the RM By Kit Palmer If there' s one motorcycle th a t can benefit from more power, it's the 1987 Suzuki RM125. The motorcycle isn't horribly slow, but a few more horsepower would definitely he lp since it already has the ' . b est.suspension pac ka ee i th e age In busi ness. Pu t the two together and you've got a motorcycle 22 you can win on. We gave our Suzuki to Pro Circuit Racing, an aftermarket motorcycle hop-up compan y that 's been involved in motocross racing for many years and has become one of the most highly respected compa nies in the busi ness. Many privateer, and even some factory motocross bikes campaigning in the National MX Series have found their way into Pro Circuit's garages in seach of more horsepower. Since the RM already has sufficient power off the bottom, most of the work done to the motor was to increase performance from midrange on up. To do this, Pro Circuit shaved off the bottom of the cylindem dropping the whole cylinder, thus lowering the intake ports. Then the transfer ports were raised and the exhaust ports enlarged. With the cylinder lowered, the head had to be mi11ed from keepi ng the pi ston from hitting the dome. The inside of the cylinder head gets polished, too. Pro Circu it replaces the stock 36mm Mikuni carburetor for a 36mm Keih in , which Pro Circuit says car bu ra tes better than the Miku ni and is easier to jet spot on. We insta11ed a half inch reed spacer between the cylinder an d the reed block. This spacer is design ed to increase bottom end. The last item to be insta11ed was a Pro Circu it exhaust pipe, which com p lements the porting and carburetion changes, as we11 as aiding in mid-range an d top-end perfor ma nce. Pro Circu it offers differen t pipes to en hance certain areas of the powerband, depending on the rider's preference. : After getting the reworked cylinder and head from Pro Circuit, the rest of the package (carburetor and pipe) bo lted right on our Suzuki without a hint of problems. The pipe fitted perfectly, but mounting the carb is a little tough with the reed spacer in place. . The pre-set Keihin carburetor was jetted right on the money, and our Suzuki went straight from the gara~e to the track with no hassles 10 between. With the Pro Circuit mod s, our Suzuki noticably gained power in the middle of the powerband and on top without losing any power off the bottom. The overa11 powerba nd was made broader an d more powerfu I. In stock condition, the Suzuki's motor is very easy to manage and is very forgiving for a 125cc rn o to crosser , an d what 's nice about the Pro Circu it setup, is that even with the horsepower increase, the Suzuki remains easy to ride. The power doesn't get peaky or explosive, instead, the characteristic of the stock powerband remains the same but there is just more power everywhere. Reliability seems to be strong, too. We've put many hard hours on the Suzuki since receiving the Pro Circuit mods, and nothing has broken or worn out prematurely. Usua11y an y kind of high tech motor hop-up isn't going to be cheap, bu t the cost of the Pro Circuit mods that were made to our bike is reasonable. The cylinder porting, head modifications, Keihin carburetor (wi th je~ and pipe costs nearly $500. For more information, contact PiR Circu it Racing, 4212 E. La Palma, Ana hei m, CA 92806. Phone 714/ 3~ 5400. • Even with all the modifications;the RM remains easy to ride.

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