It’s always fun to make your dirt bike more powerful and go faster. But, it’s difficult for many riders to choose what they want to buy for their bike because money is tight. If you own a Yamaha WR250F though, then you’re just in luck, because I would like to share a few mods that you can do to make it faster. Oh, and did I mention, they’re FREE!! So if you want to get that extra kick out of your almost-motocross-bike-but-still-a-trail-bike, then you’re in the right spot. These modifications consist of altering the air-box, exhaust, CDI wires, and the throttle stop.
The stock air-box on your WR250F dirt bike has a snorkel/shield that helps protect the air filter from water, sand, and other foreign materials. Although it is safer on your filter, it also robs usable horsepower because it blocks air-flow. To change this you just unscrew it and pull the screen out. This mod will make it more like the YZ250F because it doesn’t have the screen in it. If you go out to the desert or a dusty track and want to protect the air filter, simply screw back in the screen. Doing this will make more of a difference on the 2001 and 2002 models because the newer ones have a battery in the air-box that restrict air-flow.
The exhaust baffle on the WR250F is very restrictive because it has to be quieter and have a spark arrestor for trail riding. The exhaust hole is very small, taking away a lot of power from your dirt bike. To remove the baffle you must take off the ten-millimeter bolt on the end of the muffler that keeps it there. Then just slide out the baffle and you will have instant power gains. Although doing this give the bike more power, it will be much louder, so keep that in mind if you ride close to crabby people that don’t want people to have fun these days. If you want to buy a silencer with a spark arrestor that keeps the bike quiet, yet still gains power, an FMF Q4 slip-on exhaust is an excellent choice.
CDI Gray Wire
The gray wire on a WR250F from the CD ignition box connects to the ground. The gray wire is what makes the WR250F’s timing differ from the YZ250F. It retards the timing on the mid-to-top-end of the RPM range, thus making it a slower and more poky ride. To give it more power in the upper RPM range you simply have to get rid of the gray wire. You can either cut it, or take it off and cover it with some tape.
To get the the wire you have to take off the seat, the tank, and the radiator shrouds. Find the CDI, which is a black box (on the right side of the steering stem for ’01-’02 models). There should be two different groups of two wires coming out of the CDI. The kill switch has a black wire and a black wire with a gray stripe. You want the other group with a black wire and a gray wire. It should be under the frame where the gas tank is. Then just unplug the connector and pull of the dust ring. Plug the connector back in and tape up the wire you just took off to the connector. Then you just slap the tank, shrouds, and gas tank back on and you’re good to go!
Who wants to be restricted, especially on a dirt bike?? I know I don’t, and that’s why one of the first things I’d do on a WR250F is get rid of the ridiculous throttle stop that limits it to 3/4 throttle. To get rid of this you must go to the right side of the carburetor and take off the throttle cover that has a couple of allen bolts. The throttle is a screw on the bottom of the throttle disk, as shown in the picture. To modify it to the length of the YZF throttle stop, take it out and cut it with a saw. The original size is in between 30 and 35mm, so cut it to about 25mm. Put the throttle stop back in and that’s it.
After you do these mods your bike will be about as close to a YZF motocross bike as you can get. There are a couple more modifications you can do to your WR250F, but they require some special tools and a little extra cash. If you take out the exhaust baffle and decide that it’s too loud where you ride, you can just get a Silencer Insert for it to lower the decibels while still keeping almost all of the power. Good luck, and ride safe!
Carry your WR250F with a Motorcycle Hitch Mount.