Hints and tips for your WR400

Found this posted on http://www.geocities.com/bigblue400/. I reposted it here.

Copied from July 1999 Motocross Action magazine (MXA)

1) One of the parts that Yamaha has experienced some problems with the water pump seal. If you own a ’98 YZ400, you might consider having the seal replaced sometime this year. The ’99 water pump has a new impeller shaft with a special coating. When you replace the ’98 seal, put in a ’99 impeller shaft.

2) The MXA test crew wore out the front wheel bearings on our ’98 YZ400. The ’99 uses the same wheel bearings, so we expect to replace those bearings after one year of hard use. When replacing the front wheel bearings, be sure to replace the spacer tube between the bearings also. Why do the front wheel bearings wear out on the YZ400 but not on the YZ250 (which uses the same front wheel)? No one knows, but it probably has something to do with the YZ400’s torque-driven front-wheel steering.

3)The cooling spigot that goes into the front of the head (from the left side radiator) leaks. If your water level is chronically low, the 90-degree elbow spigot is probably leaking. Check your cylinder head immediately. The ’99 tubing is bent instead of mitered, but some early ’99 spigots still have the 90-degree miter.

4) Even if the water spigot doesn’t have a crack in it, sometimes the 6mm bolt backs out and the water leaks out behind the O-ring. When replacing the spigot, be sure to use high-temp grease on the O-rings.

5)Changing the oil after every race is the best insurance that a YZ400 owner can have, but don’t forget to remove the wire screen oil filter (in the bottom of the down tube) and clean it at least once after initial break-in (and at regular intervals during the year). If it gets clogged, it won’t matter whether the oil is new or old.

6)To drain the oil completely from the YZ400 you must: (1) Remove the drain bolt on the bottom of the frame down tube. (2) Remove the oil filter from the right side of the side cover. (3) Pull the drain plug from under the tranny. However, the majority of oil comes out of the frame down tube.

7) To check the engine oil, use the dipstick behind the steering head. Do not thread it into the frame to check the oil height. Run the motor for at least 30 seconds before checking the oil. It will not read correctly if the engine is cold (it will read low).

The MXA test crew runs 1600cc of 10W/50W Yamalube-4R.

8) There is a punch mark on the clutch pressure plate that must be lined up with a punch mark on the clutch hub before the clutch will slip back together.

9) Although blipping the throttle on a YZ400 is a big no-no (because of the accelerator pump), you should blip the throttle once or twice to squirt a small amount of fuel into the engine the first time you start it up in the morning.

10) If you think the YZ400 is loaded up, hold the compression release in, turn the throttle wide open and kick the engine through ten times. This does the same thing as using the "hot start" button but is more effective at cleaning the engine out (especially if your buddies have been playing with the throttle).

11) Do not remove the wire screen in the air box. Although four-stroke racers have always removed the air box screen from other thumpers, Yamaha claims that the screen does not cost any horsepower.

12) If you have a problem with stalling the bike in tight turns, turn the idle up to a very fast idle. Although the bike will gallop at low rpm, it will resist stalling in tight turns.

13) The MXA test crew has had great luck with flywheel weights. They do not cost horsepower, seem to increase low-end throttle response and stop the YZ400’s tendency to stall in slow corners. Flywheel weights are available in 6, 8, 10, and 12 ounce versions. We use 10 ounces.

14) There must be a shortage of grease at the Yamaha factory, because Yamaha’s come with the minimum amount of grease in the swingarm pivot, shock linkage and steering head bearings. If your local dealer didn’t grease the bike before it left the showroom (ask him), do it yourself.

15) Because the YZ400 stores hot oil in the frame, the steering head grease has a tendency to break down quickly. Steering head bearing grease must be checked regularly.

16) Do not run special high-octane race gas in your YZ400. It doesn’t need it, and the carb seals and roller bearings don’t like it.

17) The major difference between the ’98 YZ400 engine and the ’99 YZ400 engine is valve springs. The ’99 springs are longer and softer, which allows the ’99 to turn a few more rpm. It is not a big deal and the difference is almost negligible.

18) The real reason the ’99 runs better than the ’98 is that Yamaha redesigned some obscure passages in the carb to clean up last year’s jetting problem.

19) If you have a ’98 that doesn’t feel like it’s jetted properly, turn the fuel mixture screw (under the float bowl) all the way in and then out two full turns.

20) If you’d like to spin the engine over faster when kick starting it, you can use a YZ250 kickstarter. It will fit and is shorter. Some riders keep the YZ400 kickstarter stub and mount a Honda CR250 kickstarter on it.

21) Invest in a brake snake. The YZ400 rear brake pedal is prone to damage in berms.

22) If you buy a replacement oil filter from your local dealer, be sure to open the box and inspect the filter before leaving the dealership. The MXA gang has seen brand new oil filters with tears, holes and rips in them.

23) Team Yamaha riders use the clutch lever and perch from a Yamaha TZ250 road racer, but you can get similar easy-pull clutch action by switching from the stock YZ400 clutch lever to the $12 lever off of a Yamaha Banshee or XT550 street bike. The part number is (#3FY-83912-0100).

24) When you shut your engine off, bring the piston up to top dead center. This closes the valves. It’s an old BSA trick.

25) It is a good idea to loosen the bolt that holds the oil line to the back of the cylinder head (on the right rear side of the engine) after changing the oil. Loosen the bolt while the engine is running. Why? If you crack this bolt open and no oil seeps out, then the oil pump isn’t pumping or the line is clogged.

26) When you wash the YZ400, water can get in the weep hole on the right side of the cylinder head. This small hole leads directly to the spark plug well. If you spray water into this hole, the spark plug well can fill up with water, which boils when you start the engine, which creates enough pressure to blow the spark plug cap off. To avoid this, after washing your bike, blow compressed air through the hole (or put tape of the weep hole before washing).

27) The carb linkage rod that goes into the diaphragm of the accelerator pump gets corroded after multiple washings. Once a month, pull the carb off, remove the diaphragm cover (three bolts), pull the diaphragm out and polish the linkage rod. This is fairly complicated but important.

28) Do not run your compression release lever too tight. Always leave free play in your compression release lever.

29) If you run the YZR titanium subframe, check it for cracks at regular intervals. Several riders have had the upper chain roller area crack off (also, where the pipe bolts to the subframe is prone to breaking). The subframe can be welded at a shop that welds stainless steel.

30) Be careful to use the correct size spoke wrench on the aluminum spoke nipples. Most Yamaha mechanics use the wrench that comes stock in the YZ toolkit.

31) The stock airbox has Phillips head screws holding the back of the multi-piece airbox together. These screws can come loose. Check them.

32) If you run a carbon fiber rear brake master cylinder guard, you can break the master cylinder reservoir off the frame. Why? The carbon fiber guard isn’t as stout as the stock aluminum guard. When the rider’s leg hits against the weaker carbon guard, the reservoir flexes and cracks at the tab.

33) If you oil your air filter and try to start your bike – lots of luck. The wet oil on the filter will create a severely rich condition that is not conducive to lighting the fire. Oil your spare filter well in advance of putting it in the bike.

34) If you use your YZ400 exclusively for motocross, change the rear sprocket from a 49-tooth to a 50-tooth.

35) The lower shock bolt must be Loctited when put back in. If this bolt comes loose, it will destroy your shock linkage.

36) To keep your shock bolts from galling, use an anti-seize, high-temp grease on the bottom and top shock bolts.

37) What should you run in your radiator? Go to Pep Boys, buy 4 ounces of concentrated "soluble oil" and mix it with distilled water (70:1 water to oil). This eliminates radiator corrosion. You don’t need to run anti-freeze in the summer (and anti-freeze is not required if you run soluble oil).

38) The seat mount tab on the gas tank can come loose. Loctite it.

39) Replace your brake fluid (front and rear) with all-new brake fluid every six months.

40) The plastic clamp-on guides that your fork guards slide up and down in don’t have to be mounted super tight. If you put them on just tight enough that they won’t wiggle under normal action, they will self-align with the guard when you ride.

41) Silicone seal the rubber swingarm linkage caps to the swingarm. In fact, use 120-grit sandpaper to clean up the surface before siliconing the caps in place.

42) To improve braking, switch from the stock Yamaha brake hose to Fastline’s special CR-style YZ brake hose. It is shorter and runs directly to the caliper (instead of under the fork leg). If you route your brake cable Honda-style, be sure to clamp the hose securely to the fork guard.


'00 WR; YZ modified, DSP exhaust system & UNI air, Jetting by the firm of Clark, James & Bryan; really big, freakin' knee guards and no graphics. . . .

[This message has been edited by Gary Kessler (edited 09-14-2000).]

[This message has been edited by Gary Kessler (edited 09-20-2000).]

[This message has been edited by Gary Kessler (edited 09-20-2000).]

I found this piece of information on the OZ-land Thumper Forum http://www.400thumpers.oz-au.com/wr400/. Some of the information is outdated, but it is a good guide for "things to look for"!


1) Joining Link Problem

The chain guide at the rear below the swing arm has a tendency to wear out cir-clips on the chain joining link. After about 1200kms (or less if you have done a lot of riding in mud) the cir clip wears that thin that it will have fallen off. Just keep checking it the same time you change your oil, then you will be sure that you will get it in time.

2) Water Pump (98 models)

One of the parts that Yamaha has experienced some problems with the water pump seal. If you own a ’98 YZ400, you might consider having the seal replaced sometime this year. The ’99 water pump has a new impeller shaft with a special coating. When you replace the ’98 seal, put in a ’99 impeller shaft.

3) Carburettor Slide Failure

A problem that seems to be emerging with WR400's, is the carb slide. On some WR's with higher kms (7,000-8,000kms-plus) are fatiguing to the point where large pieces are breaking free and heading for the combustion chamber.

Keep an eye on the slide, and look for cracking around it's pressed oval section, and if you find any replace the slide immediately. Periodic inspections could literally save you thousands of $$$ in a worse case scenario.

4) Frayed Throttle cables

It is becoming apparent that most WR400's that have done a few kms (over 3,000kms) the throttle cables near the carburettor start to fray, and if not seen to can break.

5) Worn 4th Gear

Some WR's that have done over 10,000kms have been found to have a worn 4th gear, not badly worn or in need of replacement, just a bit more worn than the other gears. It is not to the point that you need to replace it, and it would probably last another 10,000kms.

6) Worn valve buckets

98 models had a problem of jamming valve buckets. The de-compression lever would wear the bucket that it works on, sometimes to the point of doing enough damage and jamming it. Yamaha changed the material that the buckets were made off for the 99 models, so anyone with 99 WR's onwards don't need to be concerned.

[This message has been edited by Gary Kessler (edited 09-20-2000).]

[This message has been edited by Gary Kessler (edited 09-20-2000).]

[This message has been edited by Gary Kessler (edited 09-20-2000).]

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