Okay, about 3 weeks ago I had my '03 YZ450F out. It ran fine. After my last ride, I replaced the flywheel w/a heavier one. When I fired it up (it starts fine), I cannot give it throttle. As soon as I hit the throttle, it wants to die w/a sound like a fouled plug. I changed the plug. The one that came out was pretty black. I changed back to the original flywheel...same problem. It will idle okay w/the choke on. If I take the choke off, it wants to die. I can pull in the hot start w/ the choke off and it will idle. I pretty much have to crank the idle and it's still only about right (the idle range). My only guess is that something is screwy in the carb, but I'm unsure of where to look. Anyway, choke on/off what have you, I cannot give it gas w/out it stalling. Please help! I am carb impaired so speak slowly!