wr400 wont idle

Frost, glad to see you have gotten into this one. I'm fresh out of ideas and all that I can think about is riding Jawbone cyn. tomorrow. Good luck manther. I'll check back on sunday to see how you did.

Thanks, and thanks for the help. I checked the valve clearances and the intake was perfect, right in the middle of the range specified in the manual. The exhaust was off though. They were at .33 and .30. I moved them from 178, and 179 to 180 and 181. Which put them right around .30. I plugged up the hotstart tubes, to take them out of the mix. Started it up and it definatly ran a little smoother, but still died while idling. But I had the idle way up and the pilot screw bottomed out. So it was probably pretty lean. I started trying to richen up the pilot screw some but it kept dying on me before I'd get a chance to back it out any. So I backed it out a little with the bike off then started it. But it died again. I took off the air filter, It ran a little quicker. (The revs were higher) It kept dying on me with a pop at the end. Sounds lean doesn't it? Also about that slosh or gurgle sound I described earlier... The one that occurs right after the bike dies... I've decided it is not coming from the tank or the carb. It is coming from the radiator I think.

Ok I think this is resolved, (Knock on wood). I'm pretty sure this was a combo problem. I think it was a valve clearance problem coupled with a jetting problem. First the ehaust clearance were off further than I thought. Chalk this up to me still learing how to use a valve guage correctly. (Or maybe me not using a torque wrench correctly). Second I'm still learning when it comes to jetting. And I may still not have the jetting spot on, but it's closer and the bikes idling ability is now loads better. Thanks for the help Frost Max, everyone.

Ok I think this is resolved, (Knock on wood). I'm pretty sure this was a combo problem. I think it was a valve clearance problem coupled with a jetting problem. First the ehaust clearance were off further than I thought. Chalk this up to me still learing how to use a valve guage correctly. (Or maybe me not using a torque wrench correctly). Second I'm still learning when it comes to jetting. And I may still not have the jetting spot on, but it's closer and the bikes idling ability is now loads better. Thanks for the help Frost Max, everyone.

Glad to hear that the bike is woriking better.:thumbsup:

Glad to hear that the bike is woriking better.:thumbsup:

Bike is almost dialed in... Not quite done yet though. I went riding this weekend. 100_3454.jpg

Had a blast. The bike is strong and 14 lbs lighter, with tons of power etc...

But... I always have to choke it to start it. Sometimes it takes around 3 or 4 kicks. Also if we stop to talk for a second it never fails i'm gonna stall. Not so much while idling but more so when putting around in low rpm's. Also my idle speed seems to be all over the place, sometimes it sounds high sometimes it sounds low. So... I think it's all carb / pilot circuit related. I have a #50 in there right now. "Burned" from the jetting forum was skeptical that my bike would need anything bigger than a #48. He suspected an upside down slide plate... I never took that out though. When I have a #48 in there I can't even get it to idle. I soaked the #48 in simple green overnight, then blew through it with carb cleaner several times. Still won't idle even with the pilot screw at 3, 3-1/2 turns out. Having said all that it sounds like it's running lean right? I'm gonna try the 50 at a full 2-3/4 turns. But I can't imagine I need a #52.... Maybe I need to break the carb down completely and soak it and clean it, and put it back together??? Any suggestions are welcome!

Bike is almost dialed in... Not quite done yet though. I went riding this weekend. 100_3454.jpg

Had a blast. The bike is strong and 14 lbs lighter, with tons of power etc...

But... I always have to choke it to start it. Sometimes it takes around 3 or 4 kicks. Also if we stop to talk for a second it never fails i'm gonna stall. Not so much while idling but more so when putting around in low rpm's. Also my idle speed seems to be all over the place, sometimes it sounds high sometimes it sounds low. So... I think it's all carb / pilot circuit related. I have a #50 in there right now. "Burned" from the jetting forum was skeptical that my bike would need anything bigger than a #48. He suspected an upside down slide plate... I never took that out though. When I have a #48 in there I can't even get it to idle. I soaked the #48 in simple green overnight, then blew through it with carb cleaner several times. Still won't idle even with the pilot screw at 3, 3-1/2 turns out. Having said all that it sounds like it's running lean right? I'm gonna try the 50 at a full 2-3/4 turns. But I can't imagine I need a #52.... Maybe I need to break the carb down completely and soak it and clean it, and put it back together??? Any suggestions are welcome!

I just looked back at you first post, and you said the carb had a 190 main jet in it. I wonder why that was. The bike definitely sounds lean. I can start my bike at -20 without the choke when I’m riding, so you should be able to start it at above freezing temps without choking. I know the main jet isn’t supposed to have much effect at idle and low RPM, but for me, changing the main does seem to have an effect here. Did you try a plug chop to check the main jet? Maybe a quick test would be to op in a 180 and see if anything improves.

I just looked back at you first post, and you said the carb had a 190 main jet in it. I wonder why that was. The bike definitely sounds lean. I can start my bike at -20 without the choke when I’m riding, so you should be able to start it at above freezing temps without choking. I know the main jet isn’t supposed to have much effect at idle and low RPM, but for me, changing the main does seem to have an effect here. Did you try a plug chop to check the main jet? Maybe a quick test would be to op in a 180 and see if anything improves.

Thanks Frost

Yeah your absolutley right 190 sounds way too rich. I quickly changed it to a 170 a few weeks ago, just based on the Jetting database, seems like no one runs my bike above a #175. I can go pick up a 175, 180, to try it. This is Texas, and it is already in the 80's. But I think I heard warmer temperatures means your bike is better at running lean anyway.

Thanks Frost

Yeah your absolutley right 190 sounds way too rich. I quickly changed it to a 170 a few weeks ago, just based on the Jetting database, seems like no one runs my bike above a #175. I can go pick up a 175, 180, to try it. This is Texas, and it is already in the 80's. But I think I heard warmer temperatures means your bike is better at running lean anyway.

Is it possible that the previous owner bored the engine, which may explain the large jet installed?

Is it possible that the previous owner bored the engine, which may explain the large jet installed?

Never thought of that. Also didn't realize bigger bore required a jet change. I guess it makes sense. The bigger the available amount of combustion, the more fuel will be needed. Is there an easy way to tell if the piston is bigger? Besides pulling the engine apart. Now that you mention it I do have two handwritten engravings on the side of my engine. Just some numbers.

Never thought of that. Also didn't realize bigger bore required a jet change. I guess it makes sense. The bigger the available amount of combustion, the more fuel will be needed. Is there an easy way to tell if the piston is bigger? Besides pulling the engine apart. Now that you mention it I do have two handwritten engravings on the side of my engine. Just some numbers.

The only way I know is to measure the piston, which means pulling it apart. can you call the previous owner?

I think popping in a larger main would be a good simple way to eliminate that option. You don't even have to take the carb off. Unscrew the bolt in the bottom and swap jets. Do you still have the 190 that you took out? i'd pop that in just to see if there's any improvement, or even if the bike will run. It's easier than pulling the head off to check the piston.

Have you ever done a proper plug chop to test the main jet? Run the bike at full throttle in a high gear for 10 seconds or so (in a place where it's safe to do so) and then hit the kill button and pull the clutch in so the engine dies quickly. Stop the bike, remove the sparkplug and look at the color. If it's black then the main is rich, white - the main is lean, brown - you're close, and light brown is generally considered perfect.

If your engine in modified or bored, then standard jetting data may not apply. Checking the plug like this will tell you if the jetting is right for the engine configuration.

If your bike has been bored it is not always the case that your jetting needs to be larger. A lot of 250's run larger jetting than the bigger bikes because the engines don't have the same efficiency to draw fuel through the engine. I can't help to think that your jetting still may be off. I would consider checking some of the following: was the ACV installed properly, check needle jet for wear ( I have heard of bikes running weird from that), and maybe the accelerator pump diaphram could be cracked and leaking past. What's the elevation there and the humidity? Heat causes the bike to run richer, but humidity will make it run leaner. The opposite of what you would think. I'd consider tearing apart the carb, clean it with carb cleaner(not just simple green) and blowing out the passages w/ compressed air. I'm also with Burned on the PJ size. I run 42-45. Good luck again. Bad fuel screw?

What's the elevation there and the humidity? Heat causes the bike to run richer, but humidity will make it run leaner. The opposite of what you would think. ?

Hi Max, do you mean "low humidity will make it run leaner?

Cold air and dry air are dense and will cause an engine to run lean. Hot air and high humidity are less dense and will cause an engine to run rich.

Hi Max, do you mean "low humidity will make it run leaner?

Cold air and dry air are dense and will cause an engine to run lean. Hot air and high humidity are less dense and will cause an engine to run rich.

Yes. you are correct. I guess my wording did not match the thought process. Thanks for correcting me. It's good to have knowledgeable guys, like yourself, chiming in to help brothers in need. MTR

Here's a few videos I took before I read the last couple of posts. These videos are focused on ruling out a problem with the slide plate. But if you look at 7.mov you can see the Accelerator pump in action... :^)

I'll take some pictures of the needle jet and ACV

http://www.throwhome.com/1.mov

http://www.throwhome.com/1.jpg

http://www.throwhome.com/2.mov

http://www.throwhome.com/2.jpg

http://www.throwhome.com/3.jpg

http://www.throwhome.com/3.mov

http://www.throwhome.com/4.mov

http://www.throwhome.com/5.mov

http://www.throwhome.com/6.mov

http://www.throwhome.com/7.mov

100_3511.jpg

100_3512.jpg

100_3513.jpg

100_3514.jpg

100_3515.jpg

100_3516.jpg

100_3517.jpg

100_3518.jpg

100_3519.jpg

100_3520.jpg

100_3521.jpg

100_3522.gif

100_3523.jpg

100_3524.jpg

100_3525.jpg

100_3526.jpg

100_3527.jpg

100_3529.jpg

I think you're missing the washer between the pilot screw spring and o-ring.....

I'd be installing a Zip-Ty screw to replace that one.

Also, your last video, it looks like the AP comes on really early, soaking the slide before it even opens, but then, looking at it from the other side, the slide looked higher to begin with and it looked like it timed pretty good, perfectly missing the slide....what was different?

I'm reading this thread with a lot of interest. My 400 has always ran great when warmed up, but cold it will idle and then "POP" and die. Since I put an FMF pipe on it it does this much more often and has become much harder to get started and have stay running, I have to keep revving it all the time. It dies constantly now at idle. I'm assuming I just need to play with the jetting though.

I'm reading this thread with a lot of interest. My 400 has always ran great when warmed up, but cold it will idle and then "POP" and die. Since I put an FMF pipe on it it does this much more often and has become much harder to get started and have stay running, I have to keep revving it all the time. It dies constantly now at idle. I'm assuming I just need to play with the jetting though.

Cold and a less restrictive pipe usually requires richer jetting.

I think you're missing the washer between the pilot screw spring and o-ring.....

I'd be installing a Zip-Ty screw to replace that one.

Also, your last video, it looks like the AP comes on really early, soaking the slide before it even opens, but then, looking at it from the other side, the slide looked higher to begin with and it looked like it timed pretty good, perfectly missing the slide....what was different?

Checked the microfiche, sure enough there is supposed to be some part (washer) between the spring and the o-ring. Wonder what kind of difference that would make.

Did not look at the videos yet but, the washer missing between the o ring and the spring would certainly make a difference.

If it idles better with the choke on, it's an indication you are lean with the choke off. Your red-hot header pipe is some indication of this as well, although many of these bikes will eventually heat up the headpipe. Equivalent bikes of same displacement can sometimes require different jetting combinations as well. I'd check the intake boot between carb and head, air cleaner, and then jetting. The Zip-Ty fuel adj screw is a big help. Now, when I go up significantly in altitude, all I have to do is change mainjet and fuel screw adjustment.

Good Luck.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now