need to lean out my KDX

Before you go and change the carb settings try going counter clockwise on the fuel/air screw 1/2 or a full turn. good luck

Depending on what kind of temp/humidity fluctuations we are talking about you can sometimes get by with adjusting the air screw. Many KDX owners will normally notice rising temps and humidity’s effect on jetting at lower throttle setting first so your natural response is to compensate for this by turning out the airscrew and leaning your jetting at lower throttle settings with out addressing other circuits. There are a number of reasons you see the problem at lower throttle setting first, or most noticeably. Most KDX owners ride in the woods at lower throttle settings so they wouldn’t necessarily notice if they were down a touch on power at high throttle settings. Cylinder scavenging is poor at lower engine speeds and improves as engine speed increases. Rich jetting seems to be more noticeable at low engine speeds where your already working with less than ideal cylinder scavenging. Typically lower engine speeds and low throttle setting are a package deal.

You can adjust your air screw if you need a quick fix and aren’t concerned with giving away a little power at higher engine speeds/throttle settings. In many cases through where air temps and humidity have increase substantially through the summer months you’ll need to recalibrate your carburetion. In the end you may have two of three ballpark settings you use that will allow you to run with out fouling plugs throughout out your riding season and optimize power.

I expect living in IL and close to the Great Lakes that temps are hovering around the high 80s low 90s right now and close to 100% humidity. These conditions are going to require you to do more than adjust your air screw to regain some of your lost performance. I’d follow Eric’s advice and look to the main jet and jet needle adjustments to solve your problem. You don’t say what year or size KDX you own or what jetting you’re presently running. I’m going to guess that you have a 1995 to 2003 KDX200. Typically most 200 owners will run a 155 main, stock jet needle in the mid or 2nd front the top clip position and a 45 main in temps around 70 with average humidity. Assuming this is the case I’d expect you’d be able to drop the main jet down to a 152 or 150. If your jet needle is in the mid clip position then you’ll likely want to drop it down to lean your jetting by moving the clip to the 2nd from the top position. I’d also have a 42 pilot jet in hand. Change one thing at a time and be sure to do a plug reading at WOT to insure you aren’t running lean on the main jet. Personally I’d start with a leaner main jet.

You can check out http://justkdx.dirtrider.net for more info on jetting. I’d also recommend giving Jeff at Fredette Racing Products a call. He lives close by and races a great deal in your area. He’ll very likely have an excellent starting point for your jetting.

Hope that helps,

David