FULL TEST OF THE 1998 SUZUKI RM250 THAT JEREMY MCGRATH BUILT
This archive of the 1998 Suzuki RM250 article is found in the January 1998 Issue of Motocross Action.
FULL REVEIW OF THE 1998 SUZUKI RM250 TWO-STROKE
Interested in buying a 1998 Suzuki RM250? Don’t know anything about it? Need consumer advice? These are the most common questions asked about the 1998 RM.
QUESTION ONE: IS THE 1998 SUZUKI RM250 ENGINE BETTER THAN THE ‘97?
It’s different than the ‘97. How different? Let us count the ways. (1) The exhaust porting timing and shape has been changed. (2) The power valve has returned to a single-stage unit and has been reshaped for better exhaust sealing. (3) The intake port has been enlarged. (4) The exhaust pipe is all new. (5) A flat crowned piston (it does sound impossible doesn’t it?) is used in ‘98. (6) The Keihin 38mm carb has a Power Jet. (7) The crankcases have been beefed up and crankcase inertia has been increased. (8) The reed block is larger. (9) Ignition timing has been changed. (10) Steel driven plates, paper-based drive plates and high silicon die cast clutch hub (with a steel insert) have been added to the clutch. (11) The primary gears have been surface machined to reduce noise.
QUESTION TWO: HOW FAST IS THE ‘98 RM250?
Not very fast. It has a nice, pleasant, manageable and well-placed low-to-mid powerband. The ‘98 RM makes power in the same basic window as the 1998 Kawasaki KX250, but that’s where the similarity ends. The KX is potent, powerful and violent. The RM is steady, torquey and mild-mannered.
QUESTION THREE: WHAT’S THE BEST WAY TO RIDE THE ‘98 RM250?
Suzuki ‘s 1998 power delivery is very, very midrange. It has a torquey burst of power that is limited in breadth and flexibility. It comes on off the bottom with a decent surge and does it’s best work in the middle of the powerband. The power signs off pretty quickly. The keys to going fast are to short shift, short shift and short shift again. What is a short shift? That is when the rider grabs the next gear before the rpm reaches it’s peak power point. Don’t wait for the power to top-out. Shift early and take advantage of the torque.
QUESTION FOUR: WHAT’S BAD ABOUT THE RM POWERBAND?
It limits your options. You can’t rev it out (it has no top-end). You can’t out horsepower a Honda, Kawasaki or Yamaha (it doesn’t make much in the way of ponies). You can’t pull one gear all the way down a straight (you have to short shift – which almost always means that you will be making more shifts than the competition). You can’t make a mistake (it doesn’t have a broad enough powerband to cover up a faux pas).
QUESTION FIVE: WHY IS THE ‘98 RM ENGINE SLOW?
Blame Jeremy McGrath! During the development of the ‘98 RM250 Jeremy was in the middle of contract talks with Team Suzuki. To convince SuperMac to stay on the yellow bikes, Suzuki flew special prototype cylinders over from Japan for Jeremy to try. During this testing, Suzuki, which had originally planned on sticking with the ‘97 cylinder in ‘98, decided they needed a new cylinder. Insider report that Suzuki selected one of Jeremy’s prototype cylinders based on it’s “hop-up potential.” Because of that decision, the ‘98 RM250 was delayed in production while the new cylinders were manufactured.
QUESTION SIX: SHOULDN’T THE NEW CYLINDER BE FASTER?
It should be, except for one thing —”hop-up potential” is a code phrase that means the ports have been lowered and made smaller (especially the exhaust port). When the ports are lowered an engine develops more low and midrange power at the expense of top-end. However, with a porting tool the low ports can be raised giving the mellow cylinder a much broader powerband (by holding onto some of the low-end and giving the tuner more meat to work with). For example, in ‘97 Jeremy McGrath used a ‘96 RM250 cylinder on his bike. Why? Because it had lower port heights than the ‘97 cylinder. Even more telling, Jeremy’s ‘96 cylinder then had a significant amount milled off the base to make it even lower. Once it was whittled down the cylinder was ported back up to produce a broader spread of power.
So, for ‘98 Suzuki elected to use a cylinder with lower ports. Low enough that the Team Suzuki riders (and anyone who calls a hop-up shop to have it ported) will reap major benefits. Who doesn’t benefit? Riders who are stuck with a stock ‘98 Suzuki jug. The low port heights may have “hop-up potential.” but they don’t make much power as is.
QUESTION SEVEN: WHAT ABOUT THE JETTING?
Believe it or not the Suzuki was on the lean side. This is what we ran.
Mainjet: 165 (162 stock)
Pilot jet: 45
Air screw: 1 1/2 turns out
QUESTION EIGHT: WHAT ABOUT THE REAR SUSPENSION?
Last year Suzuki blew it on the shock valving. It was jolting, abusive, rigid and harsh. Suzuki blamed the ‘97 shock disaster on Showa, claiming that the pre-production test shocks worked great, but that Showa had ruined them on the production line. What’s their excuse this year?
The ‘98 RM250 shock is jolting, abusive, rigid and harsh. It is better than the ‘97 shock, but a brick would be more resilient than that shock. Unfortunately, the ‘98’s poor damping is excuse proof. Suzuki can blame Showa once, but the second time they should have known better.
The MXA test crew is magnanimously willing to spread the blame equally between Suzuki and Showa. It’s true that the Showa shock has too much compression damping, but it is also true that Suzuki changed the shock linkage to produce a stiffer rising rate. There is plenty of blame to go around.
QUESTION NINE: WHAT WAS OUR BEST SHOCK SETTING?
The compression damping is so harsh in the second half of the stroke that the RM250 dances, kicks, bucks and boogaloos to whatever beat the terrain plays. Do yourself a big favor and send this shock to a suspension specialist. But, if you don’t have the time, money or whereabouts to send the stock shock away for remedial work try backing the compression clicker out…way out. There is nothing to be gained by running it any stiffer than 20 clicks out. Depending on track conditions we varied between 20 clicks out and 32 clicks out. If you are forced to race the shock in stock trim try these settings:
Spring rate: 4.9 kg/mm
Race sag: 102mm
Compression: 30 clicks out
Rebound: 10 clicks out
Notes: Turning the clicker all the way out is more of a psychological help than a performance one.
QUESTION TEN: HOW GOOD ARE THE 49 mm SHOWA FORKS?
Excellent (with the exception of the spring rate). They have to be to make up for the overpowering nature of the rear suspension. It’s important to note that the worse the rear suspension works, the greater the load on the front forks (because all the energy is transferred forward by the bouncing shock). The Showa forks do a passable job in stock trim, but the spring rate is not well suited to the bikes set-up. The main goal of switching to stiffer forks springs is to bring the chassis into balance.
QUESTION 11: WHAT WAS OUR BEST FORK SET-UP?
The only major change we made to our ‘98 RM250 fork was in the spring ra¯te. The stock 0.42 forks springs are too soft. They contribute to the bike’s stinkbug stance. We changed them to much stiffer 0.44’s. These are our best settings for hard-core racing:
Spring rate: 0.44 kg/mm (0.42 stock)
Oil height: 197mm
Compression: 11 clicks out
Rebound: 10 clicks out
Fork leg height: 5mm up
Notes: In stock trim the forks are the saving grace of the RM package. By stiffening the fork springs the front stays higher, which transfers more weight to the rear (to help load the over-damped shock), and stops the RM from hanging down on the entrance to turns.
QUESTION 12: WHAT ABOUT THE BRAKES?
Decent brakes. Be very careful when setting the rear brake pedal up that you leave freeplay in the slotted clevis. If you take the freeplay out of the clevis the brakes will overheat and lock solid.
QUESTION 13: WHAT ABOUT THE GEARING?
For the average rider the gearing couldn’t be worse. Second gear is almost useless for anything, but the slowest corners. The RM goes through its power so quickly in second gear that it is just a one-second gap between first and third. Third is the best gear on the ‘98 RM, but third is muted by a big gap between third and fourth. There is a major bog between three and four (especially in deep loam or under a load). The best way to maximize the short breadth of the RM’s power is to gear it down so that third gear becomes the primary gear (as opposed to second) and the 3-4 gap is narrowed.
Add one tooth to the rear sprocket, use third gear in place of second and try to short shift into fourth as soon as possible.
QUESTION 14: HOW DOES IT HANDLE?
Given the reluctant nature of the rear shock the ‘98 RM250 is lucky to handle at all. Once you stiffen up the front forks and back the clicker out on the rear shock the ‘98 RM250 is a fun bike to ride — busy, but fun. As always, it darts inside with surgical precision, turns with aplomb, feels feathery in the air and can change lines with only the slightest input.
The plus side is that it’s good in the tight stuff, excellent in the air, feels lighter than any bike on the track and perfect Supercross-style bike. The down side is that this is not a good rough track bike. It is very sketchy at speed, schizo in choppy whoops and a handful in sand. You might think that the shock is to blame for these traits, but not so — fix the rear shock and the bike’s personality won’t really change, although it will tranquilize it’s more aberrant foibles.
QUESTION 15: WHAT DID WE HATE?
The hate list:
(1) Tank decals: For some mysterious reason the Suzuki tank decals are composed of four separate pieces. We lost the chrome “RM” logo the first week.
(2) Bars: The handlebars are made of rubber.
(3) Starting: Most two-strokes start without much of a drill, but the RM lights up best with no throttle when cold and 1/8 turn when hot.
(4) Neutral: Lots of luck. Finding neutral when the engine was running was often difficult.
(5) Noise: Lots of engine clatter. It pops, bings, bams and booms for no apparent reason.
(6) Gearing: Gear it down.
QUESTION 16: WHAT DID WE LIKE?
The like list:
(1) Clutch: The RM250 gets steel drive plates, stronger clutch hub and new clutch plates. It’s not the strongest clutch in the world, but its better than the feeble effort of the last few years.
(2) Tires: Bridgestone M77/78’s
(3) Chain: It’s still a DID, but a higher grade one.
(4) Fork adjusters: We make ten compression adjustments for every rebound change. The Showa conventional forks have the compression clickers on top. That makes life easier when you are in a hurry.
(5) Shock adjusters: The shock’s rebound adjuster can be reached without having a friend press down on the rear of the bike.
(6) Flywheel inertia: Suzuki’s are famous for lack of flywheel effect, but the ‘98 RM250 is less likely to stall the motor than the ‘97 thanks to repositioning of the crank mass.
QUESTION 16: WHAT DO WE REALLY THINK OF THE RM250?
If you want to know if the ‘98 Suzuki RM250 is the Bike of the Year — it’s not. Not even close. Why not? It’s low-to-mid engine isn’t fast enough. It’s shock isn’t supple enough. It’s showroom stock set-up isn’t thought out enough. It’s outdoor handling isn’t civilized enough. All is not lost though! The RM250 may be more of a Novice-level bike than Pro bike, but with a porting tool and ten shock shims all that could change.