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Honda XR Tuning
With Scott Summers and Fred Bramblett
Honda XRs are used for everything from play riding to hare scrambles to desert racing. They are perhaps the most bulletproof and widely used dirt bikes on the planet. Although enduro and trail riders have been using XRs for decades, Scott Summers, one of the best off-road riders in the sport, has put a number one plate on the flanks of an XR600 for several times in the 1990s and has demonstrated that XRs are capable of much more than just plunking down trails or crawling through the woods. He and his mechanic Fred Bramblett are not your typical rider mechanic duo. They are motorcycle innovators. They’ve devised some interesting innovations for the XR line of Hondas. They’ve tested just about everything possible for XRs. Whether they are racing the Baja 1000, the ISDE, or cow-trailing through the deep woods of Kentucky, they know the set up that works best. Here are some of their tips on products to improve the longevity and performance of the XR line of motorcycles.
These are some of the maintenance tasks that you will need to perform after every hare scrambles race or long trail-riding weekend.
Clean the air filter and the air box after every ride. Check the filter for excess oil build-up near the point where the crankcase vent enters the air box. If the rings are worn, crankcase oil will flow up the vent and into the air box and coat the filter. This can cause a rich fuel jetting condition.
Oil and Filter
Change the crankcase oil after every two rides and the filter on every other oil change. Check the wire mesh screens that are mounted in the bottom of the frame and in the crankcase. If you ride a mud race and have to fan the clutch often, the fiber clutch plates can start to disintegrate and pollute the crankcase oil. These particles will become trapped in the wire mesh filters. You should clean these filters at least twice each year.
Lube the Cables
Lube and adjust the clutch and throttle cables. Remember that the clutch cable free-play will be reduced as the clutch plates wear.
The XRs don’t need frequent valve adjustment, but keep in mind that the valve lash will be reduced as the valve and seats wear. Check and adjust the valve lash every 200 miles or after every fifth riding weekend.
Chain and Sprockets
Clean the chain and sprockets after every ride, then lube the chain and check the free-play. Inspect the sprockets for chipped teeth, caused by rocks. Check the alignment of the rear chain guide. Sometimes rocks or ruts can bend the guide, causing the guide to push the chain out of alignment with the rear sprocket. This problem can cause the chain to derail.
Keep It Greased
The XRs have grease zerks mounted in the swingarm and linkage pivots. You should grease the zerks after every other ride for two reasons; to force water and dirt from the bearing cavity and to lube the bearing. Fred Bramblett fits grease zerks to the neck of the XR frame, to provide grease to the steering head bearings. The zerks are mounted to the frame and the races are notched to allow the grease to enter the bearing. The service interval for greasing the steering head bearings is every four rides. That may seem frequent but consider that the XR holds the crankcase oil in the frame. When the oil gets hot the frame temperature rises and the grease in the steering head bearings can melt disperse from the bearing.
Because the XR is a fairly heavy dirt bike, the spokes require frequent attention. Check the spokes after every ride and don’t be tempted to over-tighten the spokes. That can cause the rims to crack.
Change the brake fluid after every four rides. Use Dot 4 fluid.
The XR models are well-developed bikes that are extremely reliable. The one fault that even great bikes can’t escape is their ability to survive a crash. Crashing is one thing that all dirt bikers do from time to time. The rider mechanic team of Summers and Bramblett has bumped their heads together to come up with a line of products that help make the XR more resistant to crash damage. They’ve come up with some interesting innovations to improve the XRs. Their products are available through Summers Racing Concepts 1-800-221-9752
This shift and brake levers are reinforced to prevent them from bending but also designed so they break off clean to minimize damage to more expensive components. For example, the shift lever is designed to break clean at the shift shaft during really hard impacts. In that way the shift shaft doesn’t bend or damage the crankcases. A stainless steel cable wraps around the end of the levers and connects to the frame, to prevent tree branches from becoming wedged between the side covers and the levers. The cables also serve to prevent the levers from snaring when riding through deep ruts.
The Summers team noticed a common problem with XRs. It is common for the wires and rubber plug that exit from the right side engine cover to get snared by branches and yanked out of the side cover. This allows the crankcase oil to leak out of the side cover and eventually cause catastrophic engine damage. The guys developed an aluminum guard to protect the wires from tree branches. The guard just bolts on to a few of the side cover’s mounting screws, and silicone seal is applied to further insulate the wires.
The original chain guard should be modified to allow the chain to derail downward, if the chain is forced off the sprockets or breaks. It is possible for the chain to bunch-up and break the crankcases with the original guard design.
A special fork brace was developed for the conventional cartridge forks used on the XR650L, XR600, and the new XR400. The brace reduces the front wheel deflection when riding over ruts or over large rocks.
XR Performance Options
If you are considering bolt-on performance parts of high performance services for your XR, you need to consider your riding demands and the type of terrain that you ride on. There are a myriad of products available for the XR. Products designed to suit a wide variety of different applications. Here is a survey of the different engine components, and how certain products are designed for either high-speed off-road or slow-speed woods riding.
There are two ways to improve the cooling systems of air-cooled engines; welding additional fins to the head and cylinder or installing an oil cooler. The oil cooler is the most efficient set up for reducing the engine temperature. The weld-on fin set up are commonly used on desert racers that run at high speeds where there is more free air available to take advantage of the additional fins. XRs Only and Ballard Cycles sell the weld-on fin kits. Lockhart makes aftermarket oil cooler, or you can adapt the OEM oil cooler from the XR250 to the XR600.
High Compression Piston
Wiseco makes an optional high compression piston for the XR600. Higher compression pistons are generally more beneficial for slow-speed woods riding or high altitude riding.
The stock carb works great for woods riding and many riders prefer a larger 41mm carb for desert racing. The White Bros. 41mm carb kit gives an increase of about 4 horsepower and 6 mph. However, this larger carb sacrifices slow-speed throttle response that is important for woods riding over muddy or rocky terrain.
There are three types of head pipes; straight, tapered, and oversized. All OEM head pipes are straight. The XR head pipes are two different lengths. This effectively widens the powerband at low rpm with a sacrifice in peak power. The Summers team uses the tapered head pipe marketed by Yoshimura. A tapered head pipe improves scavenging efficiency and reduces pumping losses because the pipe draws out the exhaust gasses rather than relying on the piston to pump out the cylinder. Typically tapered head pipes can cause odd jetting problems but Fred Bramblett says that he hasn’t experienced any jetting problems with the Yoshimura pipe. Tapered head pipes work best with OEM cams or ones with slightly retarded exhaust timing. Oversize head pipes are generally used in conjunction with big bore kits, or for high rpm applications such as desert racing or DTX.
There are two types of tail pipes; straight through silencers and spark arrestors. Some
riding areas and racing organizations require the use of spark arrestors on off-road motorcycles. Check with the rules before you purchase an expensive aftermarket tail pipe. Straight through silencers provide the right flow characteristic and resultant backpressure to produce maximum power over a wide rpm band. Spark arrestors have a series of baffles that prevent particles of combustible gasses from exiting the tail pipe. The Summers team uses the Yoshimura tail pipe for closed course racing.
The Summers team uses the stock XR cam for hare scrambles and enduro racing, and the HRC cam for desert racing. The HRC cam has a higher lift and longer duration. Most aftermarket cams offer 2-4 degrees of duration over OEM cams. Increasing the duration generally improves peak power but changing the overlap of the intake and exhaust has a more dramatic affect on the powerband. Decreasing the overlap improves low-end torque with a sacrifice of peak power, while increasing the overlap improves peak power with a sacrifice of low-end power.