All 2st Fouled plug mystery

I'm looking for some help/advise. I have 2008 WR250 with about 100 hours on it. The bike has been bullet proof and awesome. About 4 months ago during the Atlanta summer heat and humidity, I fouled my 1st plug. I gave the carb air screw a 1/2 turn out and it ran great for 60 days. Now that the cool Fall weather is here, reset the carb and I've fouled 3 more plugs. Most of time they foul in the first five minutes but sometimes its after riding all day. The plugs don't look super wet. I'm due for a top end so could I be getting 'blow by' out of the crank? I just seams like more than a fuel mix issue?

Sounds like the same symptoms I had on my 125, I swapped every part of the electrical system and fuel system chasing it. Then put a new ring in it and no more issues. I went through 5 plugs in one 40 mile ride with the bike running great, the harder I rode it the faster they would foul. Still looking nearly new.

Later,

jmetteer - You're dead on. When I roll on the throttle hard under a heavy load and the bike is pulling a lot of torque is when I foul the plug. When I'm higher in the RPM and 'light' on the throttle, it rips... I was putting the top end off as a 'winter project' but it looks like I need to do it now.

Anyone else have an idea...

I have same bike and model and had same problems, found 1 reed petal broken

The guys at Halls said I was using the wrong plug. I have a NGK BR8es in it now. That's a resistor plug. They said to run the B8es (non-resistor). I'll try that for a few weeks...

I do run the non resistor plugs as well. Are you running the stock carb with stock jetting? My plugs were black with stock jetting. Currently I'm using the stock needle with the stock clip position, but I run 2-3 sizes smaller pilot and 1-3 sizes smaller main depending on the weather. No fouled plugs and no spooge.