When did you last clean or put new jets in and did you put in new or clean the pilots? They clog very, very easily. Your stock pilots are fine, if they are clean.
And just for the hell of it, you didn't by chance mix different types of oil in the same tank of gas? Just throwing out there!
What about switching plug wires to narrow it down a little more, determine whether or not its electrical? What you think magz?