hanging idle on 400

I'm having a problem with the idle not returning quickly enough on my '98. When shutting down the throttle ( i.e. entering a berm etc.) the rpm hang up long enough to push the bike. Any solutions?

I had a similar problem on my YZ400. It was a combination of a gummed carb linkage and the throttle cables being pinched and tweaked. I would yank the carb off and clean that rascal then as you re-assembling it you can tweak your throttle cable to where you get a good snappy throttle return. Also check your throttle housing for being clean and in the correct position on your bars. If the throttle housing is pushed to far inward on the bar the housing will rub and hang up.


Another possibility is a too lean pilot jet/screw setting. If the bike doesn't idle well try going out more turns on the pilot screw.

I have experienced the same thing on my 99 yz400. It's not that the throttle sticks or that the idle is too high. It only happens when I'm coming in to a turn really hot and snap the throttle shut suddenly. It

continues at high RPM for a second or two and then drops to idle. Thought I was imagining things but if you guys are having the same problem...hmmmm.

Have you changed your setting? The lean stock 42 pilot may tend to create the symptom you described. if you haven't played with jetting (and you should), I would recommend turning the fuel screw out (counterclock) slightly (maybe .5 turns at most for now). Or try a 45 pilot w/o changing the screw and see what happens.

Also, your accelerator pump (bottom right) could be clogged a little, slowing down the rod that regulates the extra fuel squirt. This could make fuel squirt when it should stop during the throttle roll-down period. If your bike as 500+ miles or ridden in really nasty condition, yank that carb and clean it up. Just a thought, let us know what happens.

BTW, I had the same problem when brand spankin' new. Going to a 48 pilot cured that and other lean symptoms (backfire, surging, slow to return to idle, etc).


Thanks for the advice, I'll give it a try.

The bike has less than 50 hrs. on it. When I first bought the bike it was backfiring so bad, anyone near threw themselves on the ground (BTW, the backfiring is why I acquired the bike from the previous owner with only 3hrs. on it - hah!). I dropped the clip on the needle to the very bottom slot and that cured the backfiring. I've been wanting to play with the jetting and the suspension to fine tune the bike, but I've just been havin' too much fun riding and can't seem to find the time for wrenchin'. I'll give your advice a try and see if it helps.

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