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
Trimation

Problems with YZ400

9 posts in this topic

Wondering if someone can please help me out?

I have a 1998 YZ400 that was working perfectly just a couple of weeks ago. I rode it a couple of days ago and noticed that it is cutting out in the upper parts of the gears before I should be hitting the rev limiter. I can't even go very fast on the road because it is cutting out so badly when I'm trying to hit top speeds. I thought that maybe I was getting a bad spark so I changed the plug and that seemed to make it better but it is still happening. What else could it be? What should I do?

Thanks,

Jedediah

Share this post


Link to post
Share on other sites

It could be fuel delivery, but it may also be due to a worn gear and/or bent shift fork. The upper gears can get rounded on the edges causing it to jump in and out of that gear. The symptoms can be deceiving because it makes it seem to cut out. If you are in second gear can you make it "cut out"?

Share this post


Link to post
Share on other sites
No, it only seems to do it in third, fourth, and fifth.

That sounds like the clutch slipping to me. A slipping clutch will often only show up in the higher gears.

Share this post


Link to post
Share on other sites

If it is not the 3 things that yzman has suggested, it could be your jetting. If it is getting cooler where you are, like it has here over the past 2 weeks, and you were borderline lean in the summer heat, you may be way lean now. This could cause the power "cutting out" at higher rpm's (where your main jet flows fuel) and higher load on the engine (upper rpm in higher gears.) Are you getting significant "popping" from the exhaust when you are at higher rpm and cut the throttle?

Share this post


Link to post
Share on other sites

Only does it in certain gears and only high RPM's. Thats a tell-tale sign of worn shift forks/dogs, but this problem doesn't happen overnight while the bike is in the garage.

Could be bad fuel too. Drain the tank & carb and start with some fresh 91 octane. Start simple (and cheap) and then slowly work towards other more-difficult options.

-fresh fuel

-fresh air filter

-check the spark (swap the CDI with a known working one if possible)

-clean the carb

-check timing/valves. Has the timing chain ever been replaced? It may be getting sloppy.

If none of these gain any improvment then its time to move onto more invloved troubleshooting.

Share this post


Link to post
Share on other sites

Thanks for all the replies. You've given me some things to try out. If nothing else trying them all will allow me to learn the bike better. I'll let you know what I find out.

Thanks again,

Trimation

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