2006-2014
BIG BORE KIT MONSTER
EASY BOLT-ON BIG BORE KIT


How Would You LikeTo Have the Badest KLX250S in Your Town?
Kustom Kraft Performance can turn your timid little KLX250S into a Fire Breathing 330cc Monster!
That's 80cc more displacement, OVER  30% BIGGER. 30% MORE TORQUE!

Can You Believe It?     Yes Believe It Because it's True



 

 

 

 

 

 

 

PRODUCT TEST .......KLX 250 S  330cc Big Bore Kit
From the pages of "Adventure Motorcycle/Dual Sport News"

 

 

 

 

August 2007
The Passion Behind the Power!
By: Bill Dragoo

Tim Allen said it best. All we really need is “MORE POWER!”  But how much is enough? If you’re like me, once you score another horse or two, you get over it in about a day. Then you want even more. Like the country & western song says, “I ain’t never had too much fun.” When it comes to motorcycles, Power = Fun. It’s hard to get enough.

Well, we’re in luck. The aftermarket is teeming with products and people, poised to pep up our bikes. But why? After all, the R&D going into horsepower upgrades takes skill and a strong mix of right- and left-brain thinking. Those who bore, port, polish, cam, dyno, and flow our engines could make real money doing something else. But here they are, day in, day out, UPSing our fixes to us in exchange for the right to knock another dent into our Visa cards.

True to form, soon after the green bug bit me and I fell in love with Kawasaki’s new-to-the-U.S. KLX 250 S, I discovered I wanted more than just a pretty face. I wanted to wheelie at will, roost at the twist of a wrist, and rocket out of turns with the front wheel clawing its way skyward. These things make me feel, well, younger and, if I were to be honest, maybe a little more manly.
Argh…argh…argh!

I started my quest by searching the internet for engine building experts. I found plenty of opinions about big-bore conversions, flat-slide pumper carb upgrades, exhaust mods, you name it. But I wanted to do this right. As I contacted aftermarket performance shops, I noticed a consistent thread running through the ones I liked best. These guys and gals are passionate about their work. Not only do they talk the talk, they have obviously walked the walk of quality motorcycle enhancement. They love what they do.

The first phase of the upgrade was boring. Actually it was quite interesting, but I decided to skip the popular KLX 250 cheater approach of simply swapping the quarter-liter cylinder for a stock KLX 300 jug and piston. Instead, I contacted Marvin Claridge, owner of Kustom Kraft Performance in Glenwood Springs, Colorado. Marvin brought his passion for engine building onto the scene in 2005 when Kustom Kraft’s founder, Tom Schueneman, began thinking about retirement. Marvin and Tom now work together in the business of cylinder repair, boring and recoating. Their modern facility, nestled among the Rocky Mountains, is the perfect setting for drawing talent to the flourishing industry of motorcycle and ATV performance. Kustom Kraft has maintained a reputation for quality workmanship and fair pricing since 1964, when Tom set up his first aluminum travel-trailer and peddled parts at the track.

I asked Marvin’s advice on getting more displacement from the 250. He recommended boring a stock 300 cylinder to make it a 331 and re-coating it with a Nikasil lining, which provides an alternative to the standard method of over-boring and installing a cast iron sleeve. Application is done through electrolytic deposition, much like the process used to gold-plate automotive accessories. With this method, a tough, thin layer of nickel-silicone carbide is applied to the aluminum cylinder walls. Many argue that the Nikasil coating is more durable, cooler-running, and that the cylinder walls retain lubrication better, reducing temperature and wear Marvin’s expertise and enthusiasm earned my confidence and my business. He finished the work ahead of schedule and supplied a forged J&E piston to round out the package. When I received the piston and cylinder, I checked every detail for fit, right down to ring-end gap and piston clearance. Perfect! There was not one thousandth variation from specifications.

With the larger bore, processing air through the head became more important. During my search I stumbled across Luke Heaney at Luke’s Racing in West Middlesex, Pennsylvania. Luke and his father, Mike, have been building race motors together since July of 2001. Mike has a long history as a machinist and mechanic. Both he and Luke are experts at working with nitrous oxide injection, alcohol, nitro-methane, turbochargers and superchargers, porting and flow-testing heads, high performance camshafts, tuned intake and exhaust systems. They have built their own two-stroke exhausts, modified port timing, added booster ports, changed combustion chamber shapes and compression ratios. Let me take a breath. They have modified power valves, experimented with various reed
valves, and ceramic-coated pistons. Luke and Mike have blazed the trail for those who want to make their machines run better.

Luke’s enthusiasm was infectious as we discussed my plans for the bike. Ideas popped up like dandelions in springtime and soon we decided on a course of action. I sent the KLX head to Luke. He cleaned up the ports, eliminating the rough, mass-produced castings and leaving them polished like mirrors. Luke also knife-edged the ports so airflow could split to each valve with the least possible disturbance. Finally, he performed a three-angle valve job which provided a perfect valve-to-seat contact surface.

Cams are sometimes overlooked on big bore projects, yet cam action is a critical component of performance. The people at Web Cams Incorporated know all about lift, duration, overlap, and timing. I have just enough knowledge about camshafts to embarrass myself. But when I first talked to Melissa Martinez and Faith Zeelenburg, they quickly set me straight. They saw through my guise and graciously gave me the short course to success by suggesting the Larry Roesseler grind cams. They developed these especially for Larry back when he tore up the track on his own KLX. They offered me a choice between a low- to mid-rpm cam which would provide excellent low-end grunt for woods work, and a more radical high-rpm cam for maximum overall horsepower. I chose the less aggressive grind for dual-sport riding.

Web Cams is owned by Steve Story and Laurie Dunlap. Along with sales professionals Melissa and Faith, they made quite a team on this phase of the project, taking my 900-mile cams and hard-welding, regrinding and improving them to match the work being done by Marvin and Luke. Once finished, Melissa sent my cams 3000 miles across the U.S. to Luke’s Racing, where Luke fitted them back into the head along with proper valve shims for perfect valve clearance.

I had already purchased a new Mikuni TM 33 8012, flat-slide, pumper carb, “Argh, ARGH!” I love saying that. Bill Blue, of B&B Cycle Restoration, worked my carb over by machining it to accept his new inlet and outlet adapter rings, then boring it to 34mm so that the bigger 331 could get all the go-juice it needed to really rip.

In 37 years at Cessna, Bill spent 25 years machining and 12 as a manufacturing engineer. Now retired from the manufacture of aircraft, he has set up shop in Wichita, Kansas, working exclusively on motorcycles. Bill does engine upgrades, including boring and re-sleeving cylinders, custom fabrication of stainless steel brake lines, and brackets of all kinds. His work on carburetors is impeccable. Bill and wife Jo Ann own a pair of 2006 KLX 250’s. His experience with dual-sport motorcycles places him among the finest when it comes to fitting motorcycles with the details that make them the best they can be. He sent my carb back in record time. If I hadn’t seen it before, I wouldn’t have known it had been modified. The transition from factory carburetor to his adapters is
seamless. Finally, I slapped on a Muzzy exhaust system to reduce weight and improve flow.

What’s the result of this passion behind the power? Well, the numbers don’t lie. I engaged Buddy Moore of RPM Performance Cycle in OKC to tackle the test-and-tune portion of our project. The KLX is notorious for producing a whopping 16.8 horsepower in stock form. The first dyno run netted a respectable 10-horse gain. From there, things just got better as Buddy fine-tuned the jetting, which I humbly report was pretty close from the start. I had gotten lucky, that’s all. We went up and down the scale on jet sizes as Buddy quickly learned what the KLX liked in regard to air and fuel. We tied things up with a small adjustment on the accelerator pump and gave it another run, managing to squeeze the numbers up to 28.03 at 8000 rpm. It produced 21 horses at just under 5000 rpm, five
more than the stock engine did near its 10,500 rpm maximum! Wow! My only concern was a tapering of power between 8,000 rpm and redline. Could I still be under-carbureted with the 34mm Mikuni, or was this the trade-off for choosing low-end torque over peak horsepower?

To find out, I contacted Jerry Leighton at Four Stroke Works in Hesperia, California. Jerry is known for his work with Larry Roesseler on his winning KLX. He has modified and improved parts for four-stroke motorcycles since they began replacing two-strokes at the track. Jerry immediately prepped a Keihin 35mm flat-slide pumper carb
and shipped it to me overnight.  Dyno results were almost identical. Apparently, carburetion was not the issue, at least not at the rpm range we were working within. Both carbs performed well. Further increases above 8,000 rpm would require revamping the spark advance or going to the more aggressive cams, but I had achieved my goal -- a lightweight, small bore, dual-sport motorcycle with race-worthy performance and superb rideability.

The test ride told the story. The KLX 250 S in stock form leaves something to be desired in the power department. It’s a great-looking bike, light and nimble, with good, albeit somewhat soft, suspension and great woods manners. Its dual-sport capability makes it a fantastic subject for the enhancements we chose.

When I embarked upon the maiden voyage, I broke into a smile that stuck. The bike lofted the front wheel in second gear like it was afraid to touch its knobby fingertips to the ground! Third would yield the same result with very little coaxing. Acceleration was better than brisk. It came on with a rush just above idle and kept pulling hard to 8000 rpm, still revving on out to the limit with authority. Best of all, this bike makes so much power down low that the engine doesn’t need to spin hard at all to move through the woods like the Tasmanian Devil. Am I satisfied? Heck, yes!


Thanks to the passion of these men and women, the KLX can hold its head high. It may not be a KTM killer, but it’ll sure give them a run for their money. It’s street-legal out of the box and costs a lot less, even with improvements.

There you have it. To those who say there’s no replacement for displacement, I would say that displacement has a rival. It’s the passion behind the power that maximizes performance.

View and Read all about the +-KLX Supermoto http://www.bikeland.org/story.php?storyID=52676