Why is my kdx fouling plugs "when cold"

[SWHALEY]

I have a 91 kdx that likes to foul plugs when i'm warming it up.
If I get on the throttle to hard to early my plug will foul and not restart till i put a new one in it. Could i be running to rich ?
:think:

 

[Canadian Dave]

When your engine is first started the engine internals are cold, relative to the normal temperature, and the incoming charge of fuel condenses on the engine internals as its drawn in making it hard to ignite. Applying the choke adds enough raw fuel to allow it to ignite. My point is there is a lot of fuel sitting around once the engine fires making the plug prone to fouling. You’re right rich jetting will compound the problem and make it very easy to foul a plug at start up. Check out the jetting recommendations on the JustKDX web site to get a feel whether your is in the ballpark or not. Mechanical problems like poor compression can also add to the problem.

Running a plug with too cool a heat range can also make it easy to foul plugs at start up. What heat range plug are you running? If I remember right your bike came with a BR9ES. That’s quite a cool plug. I wouldn’t hesitate to run an 8 (stock for the 95+ KDXs) and many people will run a 7 depending on their riding style and condition.

Hope that helps,

David