Many years ago the outdoor national championships were split into three separate classes, the 125cc, 250cc and 500cc or open class as some liked to call it. The 125 class was contested by the young up and comers of the sport, while the 250 and Open division championships were contested by the more experienced racers of the day. While the 125 kids would battle it out for the full length of the series on the smaller mills, the big bikes series was split into two separate championships. The 250 National title would be decided during the first half of the outdoor series and then riders would switch over to the more powerful 500cc machines to battle it out for the Open class Championship. As the years progressed, many factories began to loose interest in the open class, as sales of these high-powered machines were down and several of the companies no longer produced an open class motocross bike. Honda and Kawasaki became the only title contenders in the open class, as they were the only two manufactures that were still selling an open class motocross bike and these bikes were even dated, as the companies were no longer putting any effort into the development of these bikes. Factory riders and privateers that raced other brands that no longer built open class bikes had to drop down to the 125 class or ride highly modified 250cc machines against the powerful 500cc Hondas and Kawasaki's. As it became more apparent that the open class was doomed to become extinct, the AMA made the decision to drop the class from AMA competition and created the 125/250cc National Championships of today.
Now that the Open class is dead in AMA national competition, the question is sometimes asked, what two stroke can a guy race and be competitive with in open class race events. Yes, these events are rare, but there is one open race in the country that still thrives and that is held once a year at the Mammoth Mountain Motocross, in Mammoth Lakes California every June.
Mammoth has been a staple event on most serious racers calendar for many years and it is often appealing for riders to enter all three-displacement classes at Mammoth, to vie for the overall championship. Back in the day, Mammoth Mountain offered a large chunk of change and the prestige of being king of Mammoth to the rider that scored the best combined finishes in the 125, 250 and 500cc classes. Sure it would be easy to hop on one of the big four stroke machines that are now commonplace in today's 250cc class, but what if you are a two-stroke kind of guy, or are sponsored by a manufacture that doesn't yet offer a big displacement 4-stroke? Well, you do what many racers of the past did; you build yourself a big bore 250cc 2-stroke.
With Mammoth just around the corner, we got a phone call from our friend Jay Clark from Wiseco Piston fame. Jay just happened to be building a big bore Kawasaki 250 for just the occasion of the Mammoth race. As always, Jay wanted our feed back on his special project bike and even offered to let us enter it at Mammoth this year. How could we refuse a chance to race someone else's bike at a race such as this?
Jay started off with a box stock 2003 Kawasaki KX 250 provided by Callaway Motorsports. He first stripped the bike down to its bare frame and sent out the motor to former Kawasaki factory mechanic Tom Morgan. Tom Morgan Racing who relocated from Lake Havasu City Arizona, now in San Bernardino California, tore into the motor to create a fire breathing 327cc monster. He began by boring the cases to accept the longer (3.5mm) stroke and then blue printed the entire motor. The Hot Rod crank is stroked by moving the crank pin and welding new weights to offset the difference and is rebalanced for the new rod and huge 74mm Wiseco piston. Do to the much larger then stock piston, the cylinder is welded and stress relieved because of the large bore size. Tom completes the top-end assembly with a Cometic base spacer and a larger bore head gasket.. Now, with a whopping 54+ horsepower, Morgan opted for a larger 14-tooth counter shaft sprocket to make the KX a bit more rider friendly.
While the motor was being built at Tom Morgan Racing, Jay had the suspension over at Race Tech, where Paul Thede and the boys worked their magic. A complete revalve front and rear was done, utilizing the Race Tech Gold Valves. Spring rates were changed to a .42 up front and a 4.8 out back. Race Tech set this up based on our racers weight and skill level and based on Race Techs many years of racing experience at the Mammoth Mountain race.
While the motor was out getting some more power breathed into it and the suspension was off being massaged, Jay was hard at work assembling the chassis with its fresh B&B powder coated frame. Jay doesn't like to just build up a stock bike with a few mods. Jay likes to go all the way and turn his bikes into one off aftermarket works of art. Mr. Clark built one heck of a nice ride, using parts from many top quality manufactures in his final assembly. Although the color choice on the frame was a little bit Bling Bling for our taste, the bike had an attractive factory look to it.
Once the bike was ready for it's maiden voyage, Jay, Tom Morgan and the Race Tech boys met us out at Glen Helen Raceway for break in and some fine tuning to get ready for the Mammoth event. Initially the bike was a bit hard to start when cold due to the increased compression, but once it was warm we had little problem with starting. As we headed out on the first lap, we quickly realized that this wasn't your ordinary hopped up KX 250. With a bit more vibration then a stock 250, the 327 pulled a lot stronger throughout the power band. We could only imagine how valiant it would have been had the original 13 tooth sprocket not been swapped out for the more forgiving 14 tooth. The KX 327 was actually very rider friendly and required us to ride it the same way that we would ride our regular 250. One thing that we hoped that would have been improved over stock was the lack of top-end over rev, but the 327 still pulled short at the very top of the power band. We would most likely not have noticed this as much, but Glen Helen is famous for having ridiculously long straights that require a bike to pull long on top or to be shifted a bit more than on most tracks.
Our Race Tech suspension performed well, but would require some more time to get it dialed in for out faster more aggressive tester. As the day went on the track became much rougher and our tester became more aggressive as he got more comfortable with the bike and the track, thus requiring a different setting. This is nothing that Race Tech couldn't handle and this test gave us a good baseline for the Mammoth track. Our test crew felt that the track conditions at Mammoth would be better for the suspension settings that Race Tech provided.
Our test riders unanimously agreed that the KX 327 would be an excellent cheater bike in the 250 class, as the new 450cc 4-strokes are becoming more and more difficult to hang with on a 250cc 2-stroke. Even vet riders could take advantage of the extra HP, as many vet classes aren't restricted to motor displacement. Although we don't cheat ourselves and don't recommend cheating to anyone, it will be interesting to see what happens in the very near future, as it is fast becoming much more difficult to hang with the 450 4-strokes. With the power that the KX 327 produces and the ride ability of the complete package, this bike is a definite 4-stroke killer.
Cylinder & Head Modification/Porting and big bore of cylinder by Millennium technologies. Blue printing engine (Trans mods and matching cases) Crank Lighten, Balance and 3.5mm stroker, TMR Wiseco 74mm big bore KX piston. Cometic gasket custom head and base gaskets with spacer plate. FMF SST Pipe and spacers to a FMF Titanium silencer. A Moto Tassinari V force reed valve system (off a Jet Ski). Redline Water Wetter
This type of custom project with all of it parts from TMR isn't cheap and cost in the $2000 range. This figure is a rough estimate and would depend on how much R&D time of Tom Morgan's your looking for
This custom one-off motor is only available with all of its trick aftermarket parts from TMR. That would include; Wiseco Piston, Millennium Technologies, Cometic, FMF and Moto Tassinari
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