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.


2002 yz426 backfiring

4 posts in this topic

I'm new to the 4 stroke world. My 2002 yz426 is backfiring on deceleration and tends to idle funny. Sometimes it'll almost shut off and sometimes it'll idle higher than it should. New plug, carb was jetted according to the last owner. Any ideas?ImageUploadedByThumper Talk1462374697.562605.jpg

Share this post

Link to post
Share on other sites

First, check the idle mixture adjustment: http://www.thumpertalk.com/topic/271735-how-to-confirm-your-pilot-circuit-setting/


If that doesn't clear things up, check for air leaks, including around the fuel trim screw (the screw should have an O-ring seal on it).  If that fails, check your valve clearance.  Tight intake valves will cause this.


Note that decel backfire can be caused by the exhaust system leaking air, and commonly is.  Fix that before you dink with the carb if the first three steps give you a decent idle.

1 person likes this

Share this post

Link to post
Share on other sites

My 400 did the same thing gray is pointing you down the right path I sealed up my exhaust and set my mixture at two turns instead of 1.5 my plug now comes out good and no more back fire

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