Repair & Maintenance 2000 400ex start up September 23, 2015 I recently replaced my air cut valve as the old one was broken. I put my carb back together and now right when I start it up the idle instantly races. I do see some smoke coming out of the exhaust. Any insight would be appreciated. Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related