crazy idle yzf 400

[espotten]

Just wanted to see if anyone had any tips on why my bike will stay reved up if I give it gas in neutral? Bike takes a while to calm back down after just one rev. Can I fix this with the pilot screw and how? leaner or richer?

[grayracer513]

First look it over quickly for anything that would cause an air leak, like a loose fitting mounting sleeve, etc.

Next try setting the fuel screw according to this procedure (it's for a 250F, but it's the same deal)

http://www.thumperfaq.com/jetting.htm#PJ

If the idle does not get back to normal before you go past two turns out, you should check your valve clearances. Tight intakes will cause this.

If you still have the problem at this point, you may have an internal carb problem, such as a partially blocked pilot jet. If it ran well with the jet it now has, don't assume it's too small unless the bike has been moved to a very different environment.