HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
Get Outside

WR400 carb issue?

8 posts in this topic

I just can't figure this one out, maybe someone has some good guidance; My '99 WR400 is "missing" (coughing and spitting) when running down the road at a steady speed, between about 30 and 45 MPH (about 1/4 to 1/2 throttle) most noticably. At lower speeds (and RPMs) and when accelerating up to and over the cruising speeds, it runs like a top. Even when it's missing, if I crack the throttle, it's off like a rocket, but settle back into a steady speed and it starts back up with the missing. It's not real a real steady or cyclic "miss", and I just can't seem to narrow down what it might be. I'm thinking so far it might be a carb issue, but nothing I've done with the carb seems to change the miss. I've gone through the carb (full clean and rebuild) and I'm running good fresh gas. Any thoughts?

Share this post


Link to post
Share on other sites

WR's have a known CDI issue that is just like what you describe....but seeing as you have an older motor, I would be your carb's emulsion tube and needle are worn out.

1 person likes this

Share this post


Link to post
Share on other sites

I think I got it figured out, finally!

Thanks a bunch for the insight Krannie, I'm sure I'll be doing a jet and needle kit in the near future, but I couldn't just let it sit for another night. I went back out and took the carb off the bike and apart ...again. (I'm etting pretty darn good at this particular project!) Looking it all over, I decided to try bringing the float up a bit and that sure seems to have helped. A little frustrating when I was so sure that was not it to begin with!! (So much for "stock measurements")

Again, thanks for the help Krannie.

Share this post


Link to post
Share on other sites

The "stuttering" that you felt while cruising at a steady throttle, is very common. Some have gone so far as to replace the stock ignition system with an aftermarket one like a Dynatek. While this does fix the issue so I've been told, it is very, very costly. And some of us get our jetting dialed in, which really helps to mask the stuttering issue, and virtually makes the "stuttering" un-noticeable. I almost have to "look" for the stuttering while cruising to notice it, it lessens it so much.

Share this post


Link to post
Share on other sites

Yup, the float adjustment did it. Put a few black-top miles on it last night, and although the "studder" is still there, it is WAY LESS noticable. I figure I'll pull the carb off and apart one more time before the true riding season gets here. I plan to change up the jets and the needle, and one last tweek on the float. -Thanks for the thoughts Maniac998.

I just bought this bike this past fall to replace a much more tired old XR600. Funny thing; the kid I bought this one from said the carb had "just been rebuilt". The bike is pretty clean, but I would argue the float bowl and jets had not seen the light of day since the factory! It ran "OK" on a couple rides I got in during the fall, but I'm looking forward to this coming season and some better fuel delivery!

I'm just starting to research the jetting, so I'm certainly open to suggestions. I live in the metro Denver area and do most of my riding up in the hills west of here, usually around 8,000-12,000 ft, with a few rides each rear down at Rampart Range (around 6000 ft I think).

dad 7.jpg

Share this post


Link to post
Share on other sites

Thousands of us have had incredible results with the JD jetting kit. Others have purchased needles, pilots, leak jets, etc. individually from Yamaha and had equal success. So the choice is yours!

Share this post


Link to post
Share on other sites

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
Sign in to follow this  
Followers 0