Posted June 26, 2003 - 11:32 AM
The Yamaha WR 400 F is one of the most sought after motorcycles in recent history. Folks had deposits on the 1998 models without ever seeing one or even knowing someone that had ridden one. In 1999 the WR's didn't land on showroom floors until late April and most of them were sold. This 4-stroke motorcycle that's only been in production for two years has been bestowed by many as the best production off-road motorcycle for under $6000.00. Is there any way this bike could live up to such hype? Not a chance the way the WR is delivered from the factory. After the first ride, riders are displeased, frustrated and think they've wasted a ton of money on a timid trail bike. Rest assured you haven't pissed away money but you do need to tinker with the WR to get the fire-breathing beast to emerge from within.
How to stop the stop:
The first thing that needs to be done won't cost you a red cent. The WR comes with a handy dandy throttle stop that limits the throttle to 3/4 throttle. You need to remove this "Stop" cut it down and reinstall it.
1. Turn the gas off and run the bike until it dies.
2. On the kick-starter side of the bike on the carburetor you will see a black plastic cover. Remove the two screws and the cover.
3. Using a bungee cord wrap it around the throttle and front brake. Position the throttle 3/4 open so you can get at the small pin that limits the throttle from being opened all the way. (Note: the carb is very delicate if you don't have a small enough tool to get into the work area, remove the carb from the bike.) Using the smallest pair of pliers you can, remove the pin. This is a time consuming process but after you've shorted the stop and put it back in you'll never have to mess with it again. The pin does have lock-tight on it so taking it out isn't as easy as one would think.
4. You need to cut or grind about 8.5 millimeters off of the stop to make it 12mm long. The best way to insure you're taking off the correct amount is to open the throttle wide open and measure the distance from the base of where the stop was removed to where the roller stops. After it's been shortened, checked and rechecked, reinstall it.
Get some airflow:
The stock air filter box limits airflow to the filter. Remove the top lid from the air box to increase airflow to the carburetor. This will make your WR a bit louder but it's a necessary modification for cost free performance.
Avoid a heart attack:
After break in the first oil change is critical. Drain the oil remove the oil filter and inspect it for tears. (If there are tears get a new filter.) You will probably notice tiny pieces of metal particles captured in the oil filter. This is normal for the first few oil changes. Spray brake cleaner on the filter to dislodge particles, then use compressed air to clean everything off. Once it looks new again, reinstall it and go on with the oil change.
Don't cramp the big guy:
Larger riders find themselves cramped while sitting a top the WR. Applied Racing makes a top triple clamp mounting kit that raises the bars up and moves them forward. This helps to make the WR feel a bit roomier.
The stock seat on the WR is too firm! CEET products make a seat that is about the same density but wider on top. This gives your rear end a larger area to displace the weight. The first ride with the CEET seat leaves one thinking it's too hard. On the second ride we noticed the CEET seat was broken in and was more comfortable then the original saddle. CEET also makes a gripper seat cover that keeps you from sliding around on the seat.
WR time to YZ time:
The WR has been mellowed in comparison to the YZ400F. You can change the timing to YZ 400 specs and increase the mid rev punch and build RPM's quicker. Dave at the Southern California based Rick Peterson Motorsports was kind of enough to help us out with this conversion.
Remove the seat and fuel tank. In the manual it says to remove the radiators, you don't need to remove them. Instead remove the upper engine brackets. This will give you enough room to slide the Cylinder head cover out. Now remove the Cylinder head cover.
Remove the timing hole plugs and turn the engine until "I" is in the center of the small plug hole. At Top Dead Center the cams will be facing away from each other. The exhaust cams will have punch marks at 9:00, 12:00 and 3:00. The intake cam will have punch marks at 9:00, 12:00 and 3:00.
Remove the cam chain tensioner. Use a screwdriver to tighten the screw inside the tensioner until it locks. Then in a criss cross pattern remove the cam chain tensioner.
Loosen the cam cap bolts in a criss cross pattern and remove the cam cap. (There's a bearing retainer in the cam cap, be sure not to drop it into the motor.) Turn the exhaust cam one tooth clockwise. The timing mark on the exhaust cam will now be at 1:00. Reinstall the cam caps and torque to 7.2-ft. lb., then reinstall the cam chain tensioner and unlock it.
Smells like exhaust:
The stock exhaust is quiet but restricts airflow and performance. You can remove the inner core to achieve a better exhaust note and gain performance.At the time of this write-up the California models were not available but it's rumored the inner core can not be removed on these bikes. If your comfortable with the power of the stock exhaust system, leave it on. If you need more power an after market system is necessary.
Mounting of the Big Gun exhaust on the WR400F requires four YZ400 tail pipe mounting parts. The parts you need from the Yamaha dealer are 90387-0814J, 95024-08030, 90201-08310 and 5BE-14747-00. These parts attach the silencer to the frame.
Our friends at Big Gun Exhaust supplied us with an exhaust system for the WR400. We used Rick Peterson motorsports Dyno to test the Big Gun exhaust. As you see the Big Gun system gives the WR more usable power throughout the power band.
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