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WR400/426/450 FAQ's

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WR400/426/450 Frequently Asked Questions

Q: Why does my new WR run like an 80 rather than a 450?

A: Because the 450's are choked down with EPA-mandated restrictions. You need to do the free mods to get it to run like it was designed to. Read on newbie.

Q: What are free mods?

A: The free mods consist of the AIS removal ('05+ models), shortening the throttle stop, airbox snorkel/cutouts removal, grey wire disconnection and removal of the exhaust pea-shooter. The details for each can be found at ThumperFAQ.com. The site is primarily directed at the WR250, but the procedures are the same for the 450.

Q: I read all about the free mods and asked the dealer about them. He said it was a bad idea and that he wouldn't recommend it as it would likely void my warranty. Now what?

A: First thing, forget about the dealer, the guy is an idiot. Your warranty is only good for 30 days anyway and if you bought an extended warranty for a competition-level dirt bike, well...I won't even go there. TT is the DEFINITIVE source for accurate and experienced information on the WR. Dealers and their employees have been proven to be completely ignorant regarding their products 99.9% of the time. Trust TT, you won't be sorry.

Q: Why is my header glowing cherry red?

A: A red hot header is usually a sign of a bike that is jetted too lean, a condition almost universally found in WRs with factory-set carbs. However, the WR does not like to sit on the stand and idle. It will get hot in a hurry if it's not moving. If you're just putting around and get a red header, it's normal. Just don't put your tongue on it until it cools. If it gets red during normal riding, go fatter on your jetting.

Q: Why does my WR seem to miss when I hold the throttle steady in the 1/4 to 1/2 turn range?

A: That's your TPS (Throttle Position Sensor) doing it's job. Dirt bikes don't normally run with a steady throttle off road and they weren't designed too. Unplug it and see if the "miss" goes away. If so, then you know. You can also follow the procedure for checking the TPS voltage in the manual. It's extremely simple if you have a multimeter and some folks have found that it is set funky from the factory. Once properly adjusted, the problem goes away.

Q: What is the Accelerator Pump and why do I care?

A: The Accelerator Pump is a sub-system of the carburetor that injects a small stream of fuel into the intake side of the engine when you crack the throttle from idle. I consists of a small, secondary fuel reservoir, with a mechanical linkage that forces fuel through a small nozzle on the airbox side of the carb throat. It is important to have it properly timed per the manual, along with the proper size leak jet and diaphragm in order to get the optimum squirt duration and volume. If not, you will experience the dreaded off-idle bog. I did extensive work on this for my bike and posted my results in the jetting forum.

Q: What is a leak jet?

A: A leak jet sits in the bottom of the newer generation Keihin carbs and regulates the backflow of fuel from the accelerator pump. The standard leak jet is a 50, but the general consensus is that a 40 will make your throttle snap crisper and eliminate the dreaded off-idle bog.

Q: What is the "best" aftermarket exhaust?

A: That is like asking “what is the best flavor of ice cream”, opinions vary. Some of the more popular pipes include the FMF Powercore and Q series, ProCircuit’s T4 and 496, White Brothers E2, Yoshimura, Dr. D, GYTR or a stock YZ450 pipe. Some folks opt to simply de-restrict their stock WR exhaust and/or remove the "pea-shooter" in the tip and replace it with ProMotoBillet's silent insert.

Q: Where can I buy Yamaha OEM parts online?

A: The TT store offers them through their OEM section

Q: Will YZ plastics work on the WR?

A: Yes and No. The fenders generally will interchange with minor trimming on the rear to accommodate the coolant reservoir. The side covers are different, as the WR has the quick access air filter panel, but some members have been able to use YZ side covers with a little creative tweaking. The radiator shrouds are interchangeable with the 05 YZ on the 05 and 06 WR, but not on earlier years. As updates usually hit the YZ first, it is usually a good idea to buy plastics from a YZ a year older than the WR you’re mounting them on.

Q: What is an AIS?

A: AIS stands for Air Induction System, i.e. the smog pump. It injects air into the exhaust system to help get rid of unburned fuel for a more environmentally friendly bike. It first showed up in '05 and has been on every WR since. It can be removed and the resulting holes plugged if you buy the GYTR kit from the TT store. The GYTR Kit’s plugs are removable and also includes an adjustable needle, throttle stop and assorted items for the carb. The AIS removal DOES NOT improve performance, but it does decrease decel popping so you can more effectively jet your bike.

Q: Is a JD Jetting Kit worth it/what does it do?

A: The JD Jetting Kit contains two triple-tapered needles that are bike specific and give you a year-round solution to the WR’s jetting needs. The kit also contains an assortment of main jets and several O-rings to modify your AP linkage on the '03's and up for better throttle response.

Q: Why cut/disconnect the grey wire?

A: The grey wire mod goes hand in hand with the throttle stop mod. As you are now able to use the entire range of the throttle with a shorter stop, the ignition map must be changed to accommodate the increase in fuel delivery. Removing the grey wire connection does this.

Q: Okay, so where is the Grey Wire?

A: On the '06 and older, steel framed WR's, it's on the right side of the frame under the tank in a 6-pin connector. On the '07-up, it's under the left side panel in the 6-pin connector. The best way to do it is to push the wire out of the connector using a small slotted screwdriver and then tape off the ends. That way you can always put it back together if you want, though I don't know why you'd want to.

Q: How can I lower my bike?

A: You generally have two options available. The first is to have your suspension components professionally lowered by a suspension shop. It's expensive, but the best method. The second is to raise the forks in the clamps and buy a lowering link for the rear from a place like Mountain Motorsports. This method is quick and cheap, but your handling may suffer.

Q: What's the best method for breaking in a new WR engine?

A: Again, a very subjective question. If you’re unsure, be conservative and follow the manual. Or, do some research and decide which way you feel most comfortable with. Here is a great article to read regarding what goes on during break-in.

Q: When/How often should I check the valves?

A: Unless you’re racing, do it right after break in, somewhere in the neighborhood of 10-15 hours. After that, check it once a season. If you flog the bike, do it quarterly. One key point to remember is that the valves must be checked with the engine dead cold. The best way to do this is to let the bike sit for at least 12 hours before checking.

Q: When/How often should I change the oil?

A: With a high revving four stroke, the safest way is every 2 or 3 rides. If you’re riding dunes or in a severely dusty area, after every ride. Better to be safe than sorry.

Q: How many link pins are between the cam marks for YZ timing?

A: If you have a 400 or 426, you will need to rotate the exhaust cam sprocket 1 tooth clockwise at TDC. This will give you 12 pins between the marks, stock is 13. If you have a 450, you will need to buy a YZ exhaust cam as the rotation method does not work due to the decomp pin.

Q: What kind of oil do I use with a Rekluse?

A: According to Rekluse, they recommend Shell Rotella 5W40. However, there are some members that run other brands. The key is to use a high quality oil that does not contain friction modifiers of any kind.

Q: What is a Quickshot?

A: A Quickshot is a new cover for your Accelerator Pump that increases the amount of fuel available for the AP squirt. It is meant to cure the dreaded off-idle bog that is often found in the WR. However, there is some debate as to whether or not it really works better than a properly tuned AP circuit.

Q: What are the stock Jets in a WR450?

A: Main: 165, Pilot: 45, Starter: 65, Leak: 50, Pilot Air Jet: 80, Main Air Jet: 200(Non-adjustable)

Q: Do I need to grease a new WR?

A: Absolutely. Yamaha is notorious for using an infinitely inadequate amount of grease in the head bearings, the swingarm bearings and the shock linkage. Even though it's a pain, a new bike should be disassembled at these areas and given a generous re-greasing with a high quality, waterproof product.

Q: Can I plate my WR for road use in California?

A: Yes and No. The debate rages on with no real answer. It would seem that some folks have been successful and some folks haven't. Like all government agencies, it appears that it really depends on who is working the window that day.

Q: Which WR is Red/Green sticker compliant?

A: 98-02, 05+ are Green Sticker compliant. The 03-04 are Red Sticker bikes.

Q: How does temperature, humidity and elevation affect my jetting?

A: As temps, humidity and elevation increase, your jetting gets richer so you must jet leaner. The inverse is true as those three conditions decrease.

Lemme know what else you guys have :ride:...SC

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I exceeded the allowed character limit in the first post, so here's some more...SC


The 2007 has been assembled with a potentially deadly flaw. The centering pin on the air filter cage may have a hole down its center large enough to allow sand, dirt and/or debris to enter the carb and cylinder causing severe damage. Yamaha is aware of the problem and has a replacement part, but if you are an '07 owner, you must verify that you do not have one of the affected bikes, about a 50% rate, and get the replacement or plug the hole prior to riding. Check this thread for more details.

Q: Are there any known problems in the various generations of WRs that I should be aware of?

A: The biggest one is with the 2003 WR450. There was a problem with the e-start, primarily with the woodruff key wherein it could shear off and cause internal damage. Here is a pictorial write-up detailing the fix, complete with part numbers. The problem was fixed for '04 and the affected '03s could be fixed with upgraded parts. There is a tutorial for the upgrade available in the Performance Index. Other more minor issues include cracks in the throttle slide that could eventually cause direct metal injection into the valvetrain. This was remedied with regular inspection and replacement. There have also been a few reports of premature transmission wear that caused various gears to pop out of engagement. This was seen in several bikes that were dual-sported and then saw street use with prolonged high speed cruising in the higher gears. As these bikes were not really designed to run at constant speeds of that nature, it was not considered a surprising result.

Q: Help! My '03/'04 is puking out oil from a hole in the front of the engine...It looks like a plug or something fell out.

A: That is a little piccadillo of the 1st gen 450. The hole is where the decomp lever cable/arm/shaft used to connect when the bike was a 426/400. The TT Store sells a permanent block off plug that will remedy the problem.

Q: Why am I always getting a different reading when I check my oil?

A: The proper method for checking the oil is to run the bike for a half minute or so, shut it down and check the dipstick within 5-10 seconds. The system needs time to fill up the frame reservoir in order to get an accurate reading. If the bike has been sitting for any length of time, then the oil has begun to drain back into the sump and will give you a false low.

Q: My owner's manual says I need to use 95 octane in my WR, but all I can find is 91 or 92 at the pump. Do I have to run race fuel or an octane booster?

A: No, the manual is written for the rest of the world which uses a different formula to calculate octane. 91 or 92 octane in the US is the same as 95 everywhere else. Read this post for a more in-depth explanation and link to the full article.

Q: Can you remove the battery/starter?

A: Yes you can, but you need various parts to seal the resulting holes, and it begs the question, “Why didn’t you just get a YZ?” NCMountainman did the definitive work on this mod. Here is his quick explanation…

It’s fairly simple....take out the battery, eliminate the junction block, ground the neg lead to the frame at the voltage regulator. Wire nut/tape the positive lead. Plug the hole where the starter used to be with an automotive emergency freeze plug. Taken a step further, you can pop off the flywheel and eliminate the starter drive clutch/gears. All this also allows the use of the yz airbox (only $50, more flow and a pound less) 13 lb loss all together. Also eliminate the on/off button, just cross over the ign wires.

Q: Should I get the 250 or 450?

A: Read this, then decide.

Q: Why does my bike die when I wick open the throttle from idle or low RPM's?

A: You have the dreaded "off-idle bog". Don't worry though, everybody has it until they tune their carb. You need to read your manual and set your Accelerator Pump linkage properly. Then you need to jet your bike for the proper elevation. It's a bit of a trial and error process but your manual and the archives will help you out a ton.

Q: There's a little hole that dribbles coolant out when the bike is cold, but then it stops. What's that all about?

A: That's the weep hole designed to let you know when it's time to change out the water pump shaft and seals. It happens to all WR's eventually and is a fairly simple repair. It is designed this way so you are alerted to the problem prior to it becoming a major issue. The p/n's for the repair parts are as follows:

  1. SHAFT, IMPELLER - 5GR-12458-00-00
  2. OIL SEAL - 93109-11073-00
  3. OIL SEAL,SD-TYPE - 93102-12321-00
  4. BEARING - 93306-00105-00

Q: Can I ride Motocross with my WR?

A: Sure, but you can ride Motocross with a Trail 70 too. The real question should be, "Is the WR a good bike for Motocross?" The answer is, "Not really." Out of the box, the WR needs a lot of work to get to the MX level. You have to remember that it is a purpose-built enduro/woods/desert bike. The weight distribution, gearing and suspension are limiting factors in the MX arena. Overcome those, and you're in business. But, by the time you get those areas sorted out, you'll be out a few thousand dollars and likely wondering why you didn't buy a YZ.

Q: Why does my suspension feel soft and what can I do about it?

A: Your suspension feels soft because it is. It will especially feel soft if you came from an MX bike, as they are valved and sprung stiffer for MX-type aerials. Also, as most japanese bikes are, the bike is sprung for an average rider weight in the 165-pound range. In order to get the suspension to perform the way you want, you'll have to respring the front and rear, at the very least. If you want even more performance, then you're going to have spend some serious money and have the forks and shock professionally reworked. However, it is widely held that no matter what you do to the WR's suspension, the overall design limits what can be done and it will never be able to be brought up to current MX suspension standards.

Q: Who makes a taller/softer/lower seat?

A: Guts Racing is generally considered the best source for a replacement seat.

Q: I need a new/bigger gas tank! What are my options?

A: IMS, Clarke and Acerbis are the three big names for aftermarket fuel tanks. They will bump up your capacity to 3.1-3.3 gallons depending on brand, though there are both intermediate and ginormous sizes as well. Furthermore, unless you have an '05/'06, you will likely need to buy YZ shrouds to fit the tank, as the WR versions don't line up.

Q: I want to add a keyed ignition switch to my WR. How do I do that?

A: Those members who've wanted that extra bit of security have had success using the keyed ignition switch from a TTR. Peruse Yamaha's parts fiche to order one up and then cut and splice.

Q: Why does my engine sound like it's full of rocks?

A: There are a couple of reasons for this. One, it is full of rocks, so look for a ragged, oily hole in your case. Two, you've just grenaded your internals...look for the hole again. Three, the most likely answer, is that it's totally normal. The WR engine is noisy by nature. If you've put on a skid plate like the Flatland Racing, or the Utah Sport, it enhances the noise by reflecting it back to the rider. Don't worry, just ride, but still be cognizant of the first two answers. If it really bugs you, you can coat the inside with sound deadening compound found inside car doors prior to installation.

Q: Why is my chain chewing up my subframe?

A: Proper chain tension is crucial on any bike, but especially on the WR because of its close proximity to the subframe. Even with spot-on tension, you're still going to get some chewage. Welcome to WR ownership.

Q: I crashed and tweaked my radiator, can it be fixed?

A: There's really only one placed considered to be the best radiator repair shop and that's Mylers. Reasonable pricing, one day turn around and totally competent repair.

Q: Why do I have an oily drip coming out of the house attached to the valve cover, looping down by the frame?

A: That's the breather hose and a little drippage is normal, so don't freak.

Q: I read the whole FAQ but couldn't find the answer to my question. Now what?

A: Your next step should be to use the search engine. ThumperTalk has one of the most extensive and complete archives of any motorcycle-related website. Do a couple of searches with modified parameters and see what you come up with. Odds are you'll find what you're looking for if you employ a little creativity and motivation. Off-road motorsports are all about self-reliance and individual achievement. If you're looking to be spoon-fed, this may not be the sport for you. Most of the veteran members will be glad to help if you absolutely cannot find an answer, but do some homework first. In the end, you'll be better for it, both on the bike and off...SC

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