need some help with wr 400

11 replies to this topic
  • steveracer

Posted November 10, 2003 - 02:37 PM


i just purchaced a used wr400 and need some guidance. the bike had the airbox baffle in it and the ex.baffle,I removed them,what should I rejet the carb with.I live in pa around 600ft above sea level. Ionly rode the bike once and it was backfiring and sputtering. but it only did it some time. the previous owner removed the thorottle stop completley. the bike is very hard to start if it starts at all. but i've only had it 2 days and am new to the 4 stroke thing. any help is greatly appreciated. :)

  • faggio40

Posted November 10, 2003 - 03:03 PM


It's difficult to say by e-mail what is the problem of your bike with so few indications, moreover considering that you aren't first owner.
You have to check: plug, carb cleaning, carb setting, air filter cleaning, fuel line and thank breather.
On my bike i have this kind of problem in every ride for the first quarter of hour (when the engine is still cold)when the plug is fairly used.

  • steveracer

Posted November 10, 2003 - 03:18 PM


I put a new plug intit,new gas,I have the carb off now and the stock jetting is in it. the previous owner was not an enthusiast he didnt ride it has really low miles on it.was there any problems with this model and year 98 wr400fk.

  • Tom_Rowlee

Posted November 11, 2003 - 09:19 AM


You should not need to re-jet just for removing the air box baffel or throtel stop I have a 98 wr400 and it is a cold blooded bike but [ takes quit a few minutes to warm up ]i have found it to be bullit proof, check the spark plug / air breather . :)

  • PumpkinHumper

Posted November 11, 2003 - 09:38 AM


Correct me if I am wrong. But you are supposed to cut the throttle stop down to yz height not remove it completely. Dosn't it mess up the TPS or CDI or something if you remove it completely. Could this be some of the problems?

  • steveracer

Posted November 11, 2003 - 11:19 AM


would an 82 starter jet cause this problem? the stock size is 65. also can i buy a thorottle stop? what kind of performance gains do you get with the yz timing mod?what are the drawbacks? thanks :)

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  • PumpkinHumper

Posted November 11, 2003 - 11:52 AM


Yes you can buy the yz throttle stop.

The yz timing is really easy to do and from what I hear adds quite a bit to the wr's performance. A friend of mine just did it and loved it.

  • steveracer

Posted November 11, 2003 - 12:50 PM


I just stopped by and talked to a local mech. and he said the valve adjustment could be out. can I do this myself?

  • faggio40

Posted November 11, 2003 - 02:21 PM


Yes, it could be a problem of valve clearance... but it isn't probable... If you have a bit of practise in mecanical work in not difficult, but if you aren't, it is better a good mech.

  • steveracer

Posted November 11, 2003 - 05:34 PM


brought the bike inside to get warm(its 35 outside) and changed the plug and it fired right up. but i know i need jetting work. while i had inside i did the yz timing,what should i expect as far as jetting for yz timing mod? my jetting is stock except for needle clip in second notch from top. another thing is ,how much oil does this thing have in it? i changed the oil and it only took about 1/2 a quart with filter change. what is the gray wire mod? :)

  • PumpkinHumper

Posted November 12, 2003 - 07:09 AM


(its 35 outside)

DING DING DING.... I think you just hit the nail on the head. The older WR's for some reason my 99 yz400 included hate to run in the cold.

Part of the problem is that they take forever to get up to operating temperature. The extra capacity radiators take forever to warm up. As a result the bike will act like it is running rich and will pop like crazy. Try adding a few strips of duct tape over the finned radiator guards to stop some of the air from coming in. This will help the bike warm up faster and stay warm. Fast ridding in cold temps will actually cool the bike off too much and it will start to run like crap.

They can also be a bear to start in the cold temps. That is usually a jetting issue though. Its usually a litle lean in the winter if you havent rejeted. This will cause hard starting. One trick is to lay the bike over on its side untill it drools gas. Then try starting it. It seems to help. Maybe turn the fuel screw out 1/4 turn.

Also run thinner oil in the cold temps. This will help with the starting. When it gets close to freeaing that thick oil dont want to move. Its hard to get the bike to turn over with the oil like sludge. Try a synthetic oil if you dont already.

  • tctrailrider

Posted November 12, 2003 - 07:34 AM


how much oil does this thing have in it?

Very close to 1.5 quarts.


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