Suzuki Rm250 Two-Day Qualifier
SUZUKI RM250 TWO-DAY QUALIFIER
Before you ride for six days you must excel for two
OBJECTIVE: CONVERT A 1987 SUZUKI RM250 MOTOcross bike into a serious ISDE/two-day qualifier machine. Ron Lawson, our Managing Editor, is an excellent motocross and enduro rider who has a hankering to ride an ISDE. And knowing the difficulty of getting into the Six Days, he decided to modify an RM250 motocrosser for the two-day qualifying events, thinking that it could give him a slight edge in the crucial special-test sections.
And his Six-Days Suzuki just might give him that edge. The engine is stock internally but has a few external changes. A rejetted 38mm Keihin carburetor (for $139, with throttle cable, from Finish Line Racing Products at [714] 528-0046) has increased the throttle response at all engine speeds, while completely eliminating the Stocker’s hesitation and stumble at low rpm. The engine even will idle nicely when necessary. The new carb breathes through a Twin Air foam filter from White Bros. ([714] 895-1991) that sells for $ 15.95.
A new, $ 149.95 pipe and $49.95 oval silencer from PSI ([414] 787-2430) is fitted with a $39.95 Sparky ([714] 779-5318)—exhaust modifications that increased the engine power all across the rev range. And an additional 3Apound of ignition-rotor weight adds to the engine's lowspeed lugging ability and tractability. The steel disc used for the added weight cost less than a dollar at a local metal supply, and the necessary welding was $20. We also had to fabricate a ‘A-inch-thick ignition-cover spacer from plastic that would allow the retention of the stock cover.
The RM’s motocross gearbox is stock despite its extremely close ratios. The modified engine pulls so well at lower engine speeds that the tall first gear usually presents no problems. For really tight courses, a one-tooth-smaller countershaft sprocket lowers the overall gearing enough to let low gear handle most situations without a lot of clutch slipping. For faster, more open races, the standard gearing is fine. And to bullet-proof the final drive, we installed a DID O-ring chain ($61.89 at a local dealer) and strengthened the stock chain guide by bolting hardened aluminum sides to the plastic block.
A headlight and a taillight are required for ISDE qualifiers, but they only have to glow long enough to pass inspection each morning. Since an RM ignition has no lighting coils, it seemed a logical solution to install an ignition from a 250 Quadracer—but it won’t fit. Lawson instead solved the problem by adding “cheater lights.” These consist of a 9-volt dry-cell battery, an illuminated red rocker switch that doubles as the tailight, and a 9-volt bulb for the headlight. The whole works costs $5 at any Radio Shack. The 9-volt bulbs are fragile and require replacement before each inspection, but that only takes a few minutes. A small dentist’s mirror (about $1.50 at a drugstore) and a bicycle ringer horn ($2 at a bicycle shop or discount store) are used to comply with other equally silly two-day regulations.
The ’87 RM250 is blessed with outstanding motocross suspension that also works well off-road, so it was left alone. The fork is a little harsh on square-edged bumps and holes at slower speeds but works great at medium-tofast speeds. The rear suspension is smooth and compliant, and doesn’t kick or act nasty when bashing into rocks and tree roots.
Speeding through the trees on this modified RM is quite an experience. It is agile and small-feeling, and easy to pitch into a sudden corner. And the steering is precise without being too quick. The responsive engine lets the rider easily pop the front wheel over rocks and other obstades at racing speeds. The stock clutch is durable, but we installed Ferodo front-brake pads ($20 a pair at local dealers) that won’t give up before the end of the event like the stockers will.
To eliminate the possibility of a flat, Lawson installed a Michelin Bib Mousse solid-foam tube ([21 3] 597-0339) in both tires. These special tubes can be purchased only with Michelin tires, but Michelin doesn’t make the ecological rear tire required in all ISDE and two-day qualifier events. So Lawson bought a set of Michelin knobbies ($149 for the front, $196 for the rear, both with the solid-foam tubes), then mounted the front one and pirated the rear tire’s Bib Mousse tube so he could stuffit in a Pirelli eco tire (about $72 at most bike shops). The foam tubes reduce the possibility of getting a flat to about zero, but both tires are a little skatey on hard ground.
For better rider control and comfort, we swapped the oddly bent RM handlebar for an Answer ([805] 2574411) aluminum bar that sells for $39.95. For better rider protection, Lawson mounted several Acerbis plastic parts, available from most dealers. He used a wider front fender ($ 14), an enduro rear fender with taillight ($30.75), a set of handguards ($14.95) and a headlight/numberplate combo ($33.95). He also attached a $ 1 59 ICO electronic odometer (1-800-331-0470) that provides mileage information, although it isn't really necessary for two-day events. But the RM does need more fuel capacity, and although the slim, 3.5-gallon gas tank from IMS ([714] 781-5849) costs $ 1 50, it eliminates worries about running out of fuel between gas stops.
So far, our home-built RM250 two-day machine has proved extremely reliable and competitive in the first couple of events. We have no doubt about the RM's ability to qualify for the ISDE; the rest is up to Lawson.
