wr400 will not idle HELP!!!

I am working on a 98 wr400 for a friend of mine.... it will not idle without the choke on and seems hard to start without the choke as well. It pops and cracks when you rev it up, but runs fine once you are moving and has plenty of power. The guy who owns it said he hasnt done anything to it since he rode it last year. This problem came out of the blue.

So far this is what I have done:

1. totally disasembled carb and cleaned all jets passages and screens including the one above the float needle

2. checked all the hoses for blockage and cracks

3. drained the tank checked the petcock screen- put in new fuel

4. new spark plug

5. disconnected kill switch to eliminate grounding possibility.

I am at the end of my knowledge base.......... anyone got an idea what to do next?

thanks for any help


Mcgyver, I've seen you make nuclear bombs out of paperclips and chewing gum, what happened to your mad skillz?

Boy that was helpful.................. not. :)

Anyway yes thats how I got the nickname........ I can usually make something out of nothing, so people started asking me to come up with solutions for which nothing else would work and the mcgvr thing stuck.

But engine problems fall in a different catagory, nothing needs invented. One or more of the parts in the engine isnt doing what it should and I thought I might run across someone who has had the same problem and save this guy some money buy not having to pay a bike shop 500.00 to replace a 10.00 part.

Anway I checked the coil and cant get the resistance readings that the manual says should be there so Im going to have the coil checked out at the shop.


Are you sure you cleaned out the pilot jet?

Im real sure it was cleaned, I removed every part on the carb and blew every passage out with 25 psi and made sure the air got thru. I did the same with all the jets and hoses.

I have done this three times.... the carb is clean.

It seems like at times it will fire on two or three kicks and then it doesnt sound the same for a kick or two.

The coil readings arent right but the magneto readings are dead on.

I think its the coil :)


Is there a chance his valves are out of spec?

Come on mcgyver that was an easy joke. :)

No harm done motogoalie........ just frustrated at the time. I have taken this carb off and cleaned it 3 times and spent 5-6 hours on this beast. I hate to think it needs the valves checked I dont want to spend a ton of time on this job. Ive got to put a new clutch in the yz before the weekend and get my boys bike ready too.

It wouldnt bother me if the bike owner was interested in using the bike once it is fixed and wanted to invest some money in it. But I think I have seen him ride this bike 2times in the last 4 years. All it does is sit in his garage and get leaned on while he and his buddies drink beer and wish they had something to do. If you saw this bike you would think it was new..........spotless.

So I have been asked to fix it basically for nothing.

Man am I whinning or what....... must be the heat today. :)



Just walk away from it. To hell with it.

It's all good. I wish I had a buddy around that would trouble shoot my bike. :)

Its hard to walk away when the bike is sitting in the middle of your garage!

Its got to be something simple.

I get another day off on thursday. I'll get some advice from the local bike shop. One of the techs there has been riding dirt and street bikes since before I was born ( I'm 36 so he's been riding a long time). Anyway he's been itching to ride my Vmax since last year so I'll make a deal with him. Help me figure this out and take the 'max for a joyride. :)

Well guys I figured the idle problem out ( with some help from the guys at the bike shop. Its been a couple of weeks ago but I havent had time to get on the computer to post this.

Anyway, I took the carb in to the shop and the three of us looked at everything and agreed the carb was not the problem. Then one of the techs said "does that pilot jet hole look big enough to you?" It looked fine to me and the other guy.......... but the old guy went and plucked a bristle out of a wire brush and had me run it in and out of the jet a few times just in case. It didnt look any different to any of us. So I went home and set the carb on the bench for a week and gave up. I finally decided to put the carb back on the bike and give it back to the guy and admit failure....... So I start the bike and take it to his house......he wasnt home so I rode back home, pull it in the yard, stop and wait for the bike to die......... it idled fine. I rode it for 20-30 minutes and it never acted up again. All because of a little bristle from a wire brush.

I think it was BLASTER who asked me if I was sure I cleaned the pilot jet? I thought I had but there must have been something in there that cleaner and air could not get out. I learned something from this. I hope that I have helped someone else by sharing this story.

thanks guys

dave :)

I hate to say I told you so, but I told you so.

And it's BAMSTER not Blaster.

I hate to think it needs the valves checked I dont want to spend a ton of time on this job.

This does not take a ton of time. I rate it as a 2 beer job. 3 beers when you have to reshim, if you have the shims.


I am in the exact same boat as you, working on my friends yz400f and I cleaned the carb to adjust the needle and replace the main jet with stock size and I have it all together and it will not idle without the choke on. I guess I will be pulling it apart again and checking the pilot with a bristle.

I hope this does it too!!!

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