Hello, I recently purchased a 2004 yz250. The bike has a full rebuild, including replated cylinder (have all receipts). The compression is very good so my problem is not a worn top end. So my problem is the bike will carbon foul the sparkplug every couple rides (about 5 hours riding). When I say carbon foul I mean the plug has carbon built up on it and it is black but pretty dry (not covered in oil like most fouled plugs). The Carb has a 50 pilot, and 178 main. I am not sure the position of the needle clip. I ride a couple hundred feet above sea level at around 20 degrees celcius. I am running Motul 2t mix at 40:1. Also, I am running a br8eg sparkplug (stock) The bike smokes a fair bit and has a decent amount of spooge, so I am positive that its a little rich. The bike runs great when I'm riding it and the throttle is nice and crisp. But after multiple hours it will begin to feel boggy and then die within about 10-15 minutes. I only ride trails at an intermediate level, (varying from first gear trails to flat out on logging roads). I mostly ride in power band and the pipe is very hot after ive been riding. I believe sparkplugs carbon foul because the motor is not running hot enough, but correct me if I'm wrong. I am not sure what to do as I do not know why it is doing this! Any help would be much appreciated!!! Thanks!